Nonvolatile semiconductor memory having plural data storage portions for a bit line connected to memory cells

ABSTRACT

Data having three values or more is stored in a memory cell in a nonvolatile manner. A data circuit has a plurality of storage circuits. One of the plurality of storage circuits is a latch circuit. Another one of the plurality of storage circuits is a capacitor. The latch circuit and the capacitor function to temporarily store program/read data having two bits or more. Data held by the capacitor is refreshed using the latch circuit if data variation due to leakage causes a program. As a result, the data circuit does not become large in size even if multi-level data is used.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/073,999, filed Feb. 14, 2002 (now U.S. Pat. No. 7,177,196), which isa divisional of U.S. patent application Ser. No. 09/667,610, filed Sep.22, 2000 (now U.S. Pat. No. 6,373,746), which are based on and claimsthe benefit of priority from the prior Japanese Patent Applications No.11-275327, filed Sep. 28, 1999; and No. 11-345299, filed Dec. 3, 1999,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a nonvolatile semiconductor memory andparticularly relates to a nonvolatile semiconductor memory used as aMulti-level NAND cell type EEPROM, e.g., a four-level NAND cell typeEEPROM.

There is known, as one of nonvolatile semiconductor memories, an NANDcell type EEPROM. This EEPROM has a memory cell array consisting of aplurality of NAND cell units. Each of the NAND cell units consists of aplurality of memory cells connected in series and two select transistorsconnected to both ends of the memory cells, respectively. The NAND cellunit is connected between a bit line and a source line.

Each memory cell consists of an n channel MOS transistor having aso-called stack gate structure in which a control gate electrode isstacked on a floating gate electrode. Each select transistor consists ofan n channel MOS transistor having a structure in which an upperelectrode is stacked on a lower electrode as in the case of the memorycell. It is the lower electrode, for example, that actually functions asthe gate electrode of the select transistor.

One source region or one drain region is common to adjacent twotransistors among a plurality of transistors (memory cells and selecttransistors) in an NAND cell unit.

Now, the concrete structure of an NAND cell type EEPROM will bedescribed.

FIG. 1 shows part of a memory cell array of the NAND cell type EEPROM.

Each NAND cell unit consists of a plurality of (4, 8, 16 or the like)memory cells connected in series and two select transistors connected toboth ends of the memory cells, respectively. The NAND cell unit isconnected between bit lines BLi and source lines SL. Each of the sourcelines is connected to reference potential lines each formed of aconductive member such as polysilicon at preset positions.

The source lines SL extend in row direction, whereas the bit lines BLiand the reference potential lines extend in column direction. Contactportions on which the source line SL and the reference potential linecontact are provided at intervals at which each source line SLintersects, for example, 64 bit lines, i.e., four bit lines BL0, . . .BL63. The reference potential lines is connected to so-called peripheralcircuits provided on the peripheral section of the memory cell array.

Word lines (control gate lines) WL1, . . . and WLn extend in the rowdirection and the select gate lines SG1 and SG2 extend in the rowdirection, as well. The collection of the memory cells connected to oneword line (control gate line) WLi is called one page. Further, thecollection of the memory cells connected to the word lines WL1, . . .and WLn put between the two select gate lines SG1 and SG2 is called oneNAND block or simply one block.

One page consist of, for example, 256-byte (256×8) memory cells. Thememory cells in one page are programmed almost simultaneously. Inaddition, if one page consists of 256-byte memory cells and one NANDcell unit consists of eight memory cells, one block consists of2048-byte (2048×8) memory cells. The memory cells in one page are erasedalmost simultaneously.

FIG. 2 is a plan view of one NAND cell unit in the memory cell array.FIG. 3 is a cross-sectional view of the NAND cell taken along lineIII-III of FIG. 2. FIG. 4 is a cross-sectional view thereof taken alongline IV-IV of FIG. 2. FIG. 5 shows an equivalent circuit of the devicesof FIGS. 2 to 4.

In a p substrate (p-sub) 11-1, a so-called double-well region,consisting of an n well region (Cell n-well) 11-2 and p well region(Cell p-well) 11-3, is formed. The memory cells and select transistorsare formed in the p well region 11-3.

The memory cells and select transistors are arranged in an elementregion within the p well region 11-3. The element region is surroundedby an element separation oxide film (element separation region) 12formed on the p well region 11-3.

In this example, one NAND cell unit consists of eight memory cells M1 toM8 connected in series and two select transistors S1 and S2 connected tothe both ends of the memory cells, respectively.

Each memory cell consists of a silicon oxide film (gate insulating film)13 formed on the p well region (Cell p-well) 11-3, a floating gateelectrode 14 (14 ₁, 14 ₂ . . . 14 ₈) on the silicon oxide film 13, asilicon oxide film (inter-polysilicon insulating film) 15 on thefloating gate electrode 14 (14 ₁, 14 ₂ . . . 14 ₈), a control gateelectrode 16 (16 ₁, 16 ₂ . . . 16 ₈) on the silicon oxide film 15 and asource-drain region 19 in the p well region (Cell p-well) 11-3.

Each select transistor consists of a silicon oxide film (gate insulatingfilm) formed on the p well region 11-3, a gate electrode 14 (14 ₉, 14₁₀) and 16 (16 ₉, 16 ₁₀) on the silicon oxide film, and a source-drainregion 19 in the p well region 11-3.

The structure of the select transistor is similar to that of the memorycell for the following reason. By simultaneously forming the memorycells and the select transistors through the same process, the number ofprocess steps is intended to be reduced to thereby reduce productioncost.

One source region (n⁺ diffused layer) 19 or one drain region (n⁺diffused layer) 19 is common to adjacent two transistors among theplural transistors (memory cells and select transistors) in the NANDcell unit.

The memory cells and the select transistors are covered with a siliconoxide film (CVD oxide film) 17 formed by the CVD method. A bit line 18connected to one end of the NAND cell unit (n⁺ diffused layer 19) isarranged on the CVD oxide film 17.

FIG. 6 shows the well structure of the NAND cell type EEPROM.

In the p substrate (p-sub) 11-1, a so-called double-well region,consisting of the n well region (Cell n-well) 11-2 and the p well region(Cell p-well) 11-3, an n well region (n-well) 11-4 and a p well region(p-well) 11-5.

The double-well region is formed on a memory cell array section, and then well region 11-4 and the p well region 11-5 are formed on a peripheralcircuit section.

The memory cells are formed in the p well region 11-3. The n well region11-2 and the p well region 11-3 are set to have the same potential.

A high voltage n channel MOS transistor applied with a higher voltagethan a power supply potential is formed on the p substrate (p-sub) 11-1.A low voltage p channel MOS transistor applied with the power supplyvoltage is formed on the n well region (n-well) 11-4 and a low voltage nchannel MOS transistor applied with the power supply voltage is formedon the p well region (p-well) 11-5.

Next, the basic operation of the NAND cell type EEPROM will bedescribed.

First, to facilitate the description, the following preconditions arespecified. Two level data “0” and “1” are stored in a memory cell; astate in which the threshold voltage of the memory cell is low (e.g.,the threshold voltage is negative) is a “0” state; and a state in whichthe threshold voltage of the memory cell is high (e.g., the thresholdvoltage is positive) is a “1” state.

In an ordinary two-level NAND cell type EEPROM, a state in which thethreshold voltage of the memory cell is low is set at a “1” state andthat in which the threshold voltage is high is set at a “0” state.However, as will be described later, the present invention is mainlyintended for a multi-level (e.g., four-level) NAND type EEPROM.Considering this, it is assumed that a state in which the thresholdvoltage of the memory cell is low is a “0” state and that in which thethreshold voltage of the memory cell is high is a “1” state.

As for the memory cell, it is assumed that the “0” state is an erasestate and the “1” state is a program state. “Programming” involves“0”-programming and “1”-programming. The “0”-programming meansmaintaining the erase state (“0” state) and the “1”-programming meanschanging the “0” state to the “1” state.

Program Operation

In program operation, the potential of a bit line is set according toprogram data on a selected memory cell connected to the bit line. Forexample, if the program data is “1” (“1”-programming), the potential ofthe bit line is set at a ground potential (0V) Vss. If the program datais “0” (“0”-programming), the potential of the bit line is set at apower supply potential Vcc.

The potential of a select gate line SG1 at a bit line side (drain side)in a selected block, i.e., in an NAND cell unit including the selectedmemory cell is set at the power supply potential Vcc. The potential of aselect gate line SG2 at a source line side in the selected block, i.e.,in the NAND cell unit including the selected memory cell is set at theground potential (0V) Vss.

The potentials of select gate lines SG1 and SG2 in the unselected block,i.e., in the NAND cell unit not including the selected memory cell areall set at the ground potential (0V) Vss.

In case of “1”-programming, the ground potential (0V) Vss is transmittedto the channel of the selected memory cell in the selected block. Incase of “0”-programming, the channel potential of the selected memorycell in the selected block is Vcc−Vthsg (where Vthsg is the thresholdvoltage of the select transistor S1). Thereafter, the channel of theselected memory cell in the selected block turns into a floating statewhile maintaining the potential Vcc−Vthsg so as to cut off the selecttransistor S1 at the bit line side (drain side) in the selected block.

If the selected memory cell is not the closest to the bit line and thethreshold voltage of a memory cell positioned at the bit line side withrespect to the selected memory cell (or, at least one memory cell amonga plurality of memory cells which exist at the bit line side withrespect to the selected memory cell) is a positive voltage Vthcell, thenthe channel of the selected memory cell turns into a floating statewhile maintaining the potential Vcc−Vthcell.

Then, a program potential Vpp (e.g., about 20V) is applied to a selectedword line in the selected block, i.e., to the control gate electrode ofthe selected memory cell. An intermediate potential Vpass (e.g., about10V) is applied to unselected word lines in the selected block, i.e.,the control gate electrodes of unselected memory cells.

At this moment, the channel potential of the selected memory cell towhich “1”-programming is conducted, is the ground potential (0V) Vss.Due to this, a high voltage necessary for the “1”-programming is appliedbetween the floating gate electrode and the channel (Cell p-well) of thememory cell and electrons move from the channel to the floating gateelectrode by F-N tunnel effect. As a result, the threshold voltage ofthe selected memory cell rises (e.g., moves from a negative value to apositive value).

On the other hand, the channel potential of the selected memory cell towhich “0”-programming is conducted, is Vcc−Vthsg or Vcc−Vthcell and thechannel is in a floating state. Due to this, if either Vpp or Vpass isapplied to the word line, the channel potential rises by the capacitivecoupling between the control gate electrode and the channel. As aresult, a high voltage necessary for “1”-programming is not appliedbetween the floating gate electrode and the channel (Cell p-well) andthe threshold voltage of the selected memory cell is kept in a presentstatus (the memory cell is kept in an erase state).

Erase Operation

Data erase is carried out in block units and data on memory cells in aselected block are erased almost simultaneously.

Concrete erase operation will be described below.

First, the potentials of all word lines (control gate electrodes) in aselected block are set at 0V and the potentials of all word lines(control gate electrodes) of unselected blocks and all select gate linesin all blocks are set at an initial potential Va and then set in afloating state.

Thereafter, a high voltage Vpp (e.g., about 20V) is applied to the pwell region (Cell p-well) and the n well region (Cell n-well) for eraseoperation.

At this moment, as for the memory cells in the selected block, since thepotentials of the word lines (control gate electrodes) are 0V and thoseof the well regions are VppE, a sufficiently high voltage is appliedbetween the control gate electrodes and the well regions for eraseoperation.

Accordingly, in the memory cells in the selected block, electrons in thefloating gate electrodes move to the well regions and the thresholdvoltages of the memory cells decrease (e.g., the threshold voltagesbecome negative) by the F-N tunnel effect.

On the other hand, the potentials of all word lines in the unselectedblocks rise from the initial potential Va to VppE or a potential closeto VppE by the capacitive coupling between the word lines and the wellregions. Likewise, the potentials of all select gate lines in all blocksrise from the initial potential Va to VppE or a potential close to VppEby the capacitive coupling between the select gate lines and the wellregions.

Accordingly, in the memory cells in the unselected blocks, a highvoltage sufficient for data erase is not applied between the controlgate electrodes and the well regions. That is, since electrons withinthe floating gate electrodes do not move, the threshold voltages of thememory cells have no change (the present state is maintained).

Read Operation

Data read is carried out by changing the potentials of bit linesaccording to memory cell data and by detecting the potential change.

First, a bit line (or part of bit lines if all bit lines or a bit lineshield read method or the like is adopted) to which a memory cell whichdata is to be read is connected, is precharged, the potential of the bitline is set at a precharge potential, e.g., the power supply potentialVcc and the bit line is then turned into a floating state.

Thereafter, the potential of the selected word line, i.e., the potentialof the control gate electrode of the selected memory cell is set at 0V,those of unselected word lines (or the control gates of unselectedmemory cells) and of the select gate lines are set at the power supplypotential Vcc (e.g., about 3V), and those of the source lines are set at0V.

At this time, if selected memory cell data is “1” (the threshold voltageVth of the memory cell satisfies Vth>0), the selected memory cell isturned off and the potential of the bit line to which this memory cellis connected is, therefore, kept a precharge potential (e.g., the powersupply potential Vcc).

On the other hand, if the selected memory cell data is “0” (thethreshold potential Vth of the memory cell satisfies Vth<0), theselected memory cell is turned on. As a result, the charges of the bitline to which the selected memory cell is connected are discharged andthe potential of the bit line decreases from the precharge potential byΔV.

In this way, the potential of the bit line changes according to thememory cell data. Thus, if this change is detected by a sense amplifiercircuit, the memory cell data can be read.

Meanwhile, so-called multi-level NAND cell type EEPROMs have beendeveloped and put to practical use with a view of increasing one-chipmemory capacity and reducing cost per bit.

In case of the above-stated NAND cell type EEPROM, binary (one-bit) data(“0”, “1”) can be stored in a memory cell. An n-level NAND cell typeEEPROM, where n is a natural number of not lower than 3 is, by contrast,characterized in that n-level data can be stored in a memory cell.

In case of an four-level NAND cell type EEPROM, for example, four-level(2-bit) data (“00”, “01”, “10”, “11”) can be stored in a memory cell.

The prior art multi-level NAND cell type EEPROM is described in, forexample, Reference 1 (Japanese Patent Application No. 8-98627).

Normally, in the n-level NAND cell type EEPROM, a plurality of latchcircuits are provided per bit line connected to a selected memory cell.Namely, if n-level data are programmed into or read from a selectedmemory cell, the plural latch circuits function to temporarily store then-level data.

As described in Reference 1, for example, in the four-level NAND celltype EEPROM, two latch circuits corresponding to one bit line connectedto a selected memory cell are provided so as to temporarily storefour-level (two-bit) data during program or read operation.

However, as shown, for example, in FIG. 7, each latch circuit consistsof SRAM (static RAM) cells. Further, the latch circuit consisting of theSRAM cells is large in area. In addition, if the quantity of data storedin one memory cell increases (the value of n is higher), the number oflatch circuits provided per bit line connected to the selected memorycell increases, as well.

In case of the four (=2²)-level NAND cell type EEPROM, for example, twolatch circuits are provided per bit line connected to a selected memorycell. In an eight (=2³)-level NAND cell type EEPROM, three latchcircuits are provided per bit line connected to a selected memory cell.

Accordingly, if data stored in the memory cell are multi-level (n-level)data and the number of n increases, the number of latch circuits (SRAMcells) on a memory chip increases and the area of the chipdisadvantageously increases.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made to solve the above-stateddisadvantages. It is, therefore, an object of the present invention toprovide a data circuit (a storage circuit temporarily storingmulti-level data during program/read operations) which can prevent achip area from extremely increasing even if data stored in a memory cellis multi-level data.

A nonvolatile semiconductor memory according to the present inventioncomprises a memory cell section including at least one memory cell; abit line connected to the memory cell section; and a data circuitconnected to the bit line, the data circuit storing program/read datahaving two bits or more, wherein the data circuit includes the firstcapacitor storing the first data and the first latch circuit storing thesecond data.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a circuit diagram showing the memory cell array of an NANDcell type EEPROM;

FIG. 2 is a plan view showing the device structure of an NAND cell unit;

FIG. 3 is a cross-sectional view taken along line III-III of FIG. 2;

FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 2;

FIG. 5 shows an equivalent circuit of the NAND cell unit shown in FIG.2;

FIG. 6 shows the well structure of the NAND cell type EEPROM;

FIG. 7 shows a conventional data circuit;

FIG. 8 shows the outline of a multi-level NAND cell type EEPROMaccording to the present invention;

FIG. 9 shows a data circuit in the memory shown in FIG. 8;

FIG. 10 shows a memory cell array in the memory shown in FIG. 8;

FIG. 11 shows a part of a column decoder in the memory shown in FIG. 8;

FIG. 12 shows a batch detection circuit in the memory shown in FIG. 8;

FIG. 13 shows a word line control circuit in the memory shown in FIG. 8;

FIG. 14 shows a device structure in the first memory cell block shown inFIG. 13;

FIG. 15 shows a device structure in the second memory cell block shownin FIG. 13;

FIG. 16 shows a row address decoder RADD1 shown in FIG. FIG. 13;

FIG. 17 shows a word line driver RMAIN1 shown in FIG. 13;

FIG. 18 shows a row address decoder RADD2 shown in FIG. 13;

FIG. 19 shows a word line driver RMAIN2 shown in FIG. 13;

FIG. 20 shows the relationship between four-level data and the thresholdvoltages of memory cells;

FIG. 21 shows the threshold voltage distribution of memory cells afterprogramming even page data;

FIG. 22 shows the threshold voltage distribution of memory cells afterprogramming odd page data;

FIG. 23 is a waveform view showing operation timing relating to the readof even page data;

FIG. 24 is a waveform view showing operation timing relating to the readof even page data;

FIG. 25 shows the outline of read operation to even page data;

FIG. 26 is a waveform view showing operation timing relating to the readof odd page data;

FIG. 27 shows the outline of read operation to odd page data;

FIG. 28 is a flow chart showing even page data program operation;

FIG. 29 is a waveform view showing operation timing relating to thesupply of a program pulse during program operation;

FIG. 30 shows the outline of the supply of a program pulse during theprogram operation;

FIG. 31 is a waveform view showing operation timing relating to “10”verify read during the program operation;

FIG. 32 shows the outline of “10” verify read during the programoperation;

FIG. 33 is a waveform view showing operation timing relating to “Programcompletion detection” during the program operation;

FIG. 34 shows the outline of “Program completion detection” during theprogram operation;

FIG. 35 is a flow chart showing odd page data program operation;

FIG. 36 is a waveform view showing operation timing relating to“Internal Data Load 1st/3rd Quarters” during the program operation;

FIG. 37 is a waveform view showing operation timing relating to“Internal Data Load 2nd/4th Quarters” during the program operation;

FIG. 38 shows the outline of “Internal Data Load 1st Quarter” during theprogram operation;

FIG. 39 shows the outline of “Internal Data Load 2nd Quarter” during theprogram operation;

FIG. 40 shows the outline of “Internal Data Load 3rd Quarter” during theprogram operation;

FIG. 41 shows the outline of “Internal Data Load 4th Quarter” during theprogram operation;

FIG. 42 is a waveform view showing operation timing relating to “01”verify read during the program operation;

FIG. 43 shows the outline of “01” verify read during the programoperation;

FIG. 44 is a waveform view showing operation timing relating to “00”verify read during the program operation;

FIG. 45 shows the outline of “00” verify read during the programoperation;

FIG. 46 is a waveform view showing operation timing relating to thesupply of an erase pulse during erase operation;

FIG. 47 is a waveform view showing operation timing relating to eraseverify read during the erase operation;

FIG. 48 is a waveform view showing operation timing relating to “Erasecompletion detection” during the erase operation;

FIG. 49 is a waveform view showing operation timing relating to “DRAMBurn-in”;

FIG. 50 is a waveform view showing operation timing relating to therefresh of a DRAM cell;

FIG. 51 shows a modification of the data circuit shown in FIG. 9;

FIG. 52 shows an ordinary program sequence for a plurality of pages;

FIG. 53 is a program sequence for a plurality of pages if the datacircuit shown in FIG. 51 is used;

FIG. 54 is a waveform view showing operation timing for data input intoa write cache in the data circuit shown in FIG. 51;

FIG. 55 is a waveform view showing operation timing for data transferfrom the write cache to the latch circuit shown in FIG. 51;

FIG. 56 is a waveform view showing operation timing relating to therefresh of data in the write cache in the data circuit shown in FIG. 51;

FIG. 57 shows a modification of the data circuit shown in FIG. 9;

FIG. 58 is a waveform view showing operation timing for data input intoa write cache in the data circuit shown in FIG. 57;

FIG. 59 is a waveform view showing operation timing for data transferfrom the write cache to the latch circuit shown in FIG. 57;

FIGS. 60A to 60D show the gist of the present invention (ConcreteExample 1) relating to program speed;

FIG. 61 shows the chip layout of a two-level NAND cell type EEPROMaccording to the present invention;

FIG. 62 shows one example of a data circuit in the memory shown in FIG.61;

FIG. 63 shows the detail of the operation of the present inventionrelating to Data Load;

FIG. 64 is a waveform view showing operation timing relating to DataLoad;

FIG. 65 is a waveform view showing operation timing relating to DataLoad;

FIG. 66 is a waveform view showing operation timing relating to thesupply of a program pulse;

FIG. 67 is a waveform view showing operation timing relating to refresh;

FIG. 68 is a waveform view showing operation timing relating to thesupply of a program pulse;

FIG. 69 is a waveform view showing operation timing relating to programdata transfer;

FIG. 70 is a waveform view showing operation timing relating to verifyread;

FIG. 71 is a waveform view showing operation timing relating to thesupply of a program pulse;

FIG. 72 is a waveform view showing operation timing relating to programdata transfer;

FIG. 73 is a waveform view showing operation timing relating to verifyread;

FIG. 74 shows the gist of the present invention (Concrete Example 2)relating to program speed;

FIG. 75 shows the detail of the operation of the present inventionrelating to program speed;

FIG. 76 shows the detail of the operation of the present inventionrelating to program speed;

FIG. 77 shows the detail of the operation of the present inventionrelating to program speed; and

FIG. 78 shows a modification of the present invention (Concrete Example2) relating to program speed.

DETAILED DESCRIPTION OF THE INVENTION

A nonvolatile semiconductor memory of the present invention will bedescribed-below in detail with reference to the accompanying drawings.

[Preconditions]

First, to facilitate understanding the description to be given below,preconditions will be specified as follows. It is noted that thesepreconditions are intended to facilitate understanding the descriptiononly and that the present invention is realized on conditions other thanthese preconditions.

The present invention is directed to a nonvolatile semiconductor memoryfor storing n-level data, where n is a natural number of not lower than3. In the following embodiments, a four-level NAND cell type EEPROM willbe described to represent such nonvolatile semiconductor memories.

It is assumed that four-level data, “00”, “01”, “10” and “11”, arestored in a memory cell. It is also assumed that a state in which thethreshold voltage of the memory cell is the lowest (e.g., a thresholdvoltage is negative) is data “11” (or a “0” state), a state in which thethreshold voltage of the memory cell is the second lowest (e.g., thethreshold voltage is positive) is data “10” (or a “1” state), a state inwhich the threshold voltage of the memory cell is the third lowest(e.g., the threshold voltage is positive) is data “00” (or a “2” state),and a state in which the threshold voltage of the memory cell is thehighest (e.g., the threshold voltage is positive) is data “01” (or a “3”state).

In addition, since it is assumed that four-level data are stored in amemory cell, odd page data program/read operations and even page dataprogram/read operations are required. Here, among data “**”, it isassumed that the left “*” is odd page data and the right “*” is evenpage data.

Further, as for the state of a memory cell, it is assumed that a statein which data “11” is stored is an erase state, and states in which data“10”, “00” and “01” are stored are program states.

[Outline]

FIG. 8 is a block diagram showing the important parts of a four-levelNAND cell type EEPROM according to the present invention.

Reference symbol 1 denotes a memory cell array. The memory cell array 1has a plurality of memory cells connected in series and two selecttransistors connected to both ends of the memory cells, respectively.The concrete structure of the memory cell is shown in FIGS. 61 to 63.

The structure and equivalent circuit of the memory cell array 1 arealmost the same as those of a two-level NAND cell type EEPROM exceptthat each memory cell stores four-level data in the four-level NAND celltype EEPROM.

A data circuit 2 includes a plurality of storage circuits. The datacircuit 2 will be described in detail later. The function of the datacircuit will be described herein briefly.

The data circuit 2 includes storage circuits temporarily storing two-bit(four-level) read data during read operation. To be specific, twostorage circuits per bit line connected to a selected memory cell areprovided.

One of the two storage circuits temporarily stores odd page data. Theother storage circuit temporarily stores even page data. The odd/evenpage data stored in these two storage circuits are programmed into thememory cell during program operation and outputted from a memory chip 11during read operation.

A word line control circuit 3 includes a low address decoder and a wordline driver. The word line control circuit 3 controls the potential ofeach word line in the memory cell array 1 based on an operation mode (aprogram mode, an erase mode, a read mode or the like) and a row addresssignal. The word line control circuit 3 will be described later indetail.

A column decoder 4 selects a column of the memory cell array 1 based ona column address signal.

During program operation, input data is inputted into storage circuitsin the data circuit which storage circuits belong to the selectedcolumn, through a data input/output buffer 7 and an I/O sense amplifier6. During read operation, output data from the storage circuits in thedata circuit which storage circuits belong to the selected column isoutputted externally of the memory chip 11 through the I/O senseamplifier 6 and the data input/output buffer 7.

The row address signal is inputted into the word line control circuit 3through an address buffer 5. The column address signal is inputted intothe column decoder 4 through the address buffer 5.

A well potential control circuit 8 controls the potential of a cell wellregion (e.g., a double-well region consisting of an n well and a p well)in which memory cells are arranged based on an operation mode (a programmode, an erase mode, a read mode or the like).

A potential generating circuit (booster) 9A generates, for example, aprogram potential Vpp (e.g., about 20V) and a transfer potential Vpass(e.g., about 10V) during the program operation. These potentials Vpp andVpass are allotted to a plurality of word lines in, for example, aselected block by a switching circuit 9B.

The potential generating circuit 9A also generates, for example, anerase potential VppE (e.g., about 20V) during the erase operation andapplies the potential VppE to the cell well region (both the n well andthe p well) in which the memory cells are arranged.

A batch detection circuit 10 verifies whether or not predetermined datahas been correctly programmed into a memory cell during the programoperation, and also verifies whether or not the memory cell data hasbeen successfully erased during the erase operation.

The first feature of the present invention lies in the data circuit 2.Namely, as will be described in detail, at least one of a plurality ofstorage circuits arranged in the data circuit and used to temporarilystore multi-level data (n-level data), is constituted by a DRAM cell(capacitor). If two storage circuits are used to temporarily storefour-level data in, for example, the four-level NAND type EEPROM, one ofthe storage circuits is an SRAM cell (latch circuit) and the other is aDRAM cell.

As is well known, the area of the DRAM (dynamic RAM) cell is smallerthan the area of the SRAM (static RAM) cell. Due to this, inconsideration of the n-level NAND cell type EEPROM, where n is a naturalnumber of not lower than 3, if part of the plural storage circuits isconstituted by a DRAM cell, it is possible to decrease the area of thedata circuit 2 compared with a case of constituting all storage circuitsonly out of SRAM cells as shown in a conventional semiconductor memory.

The second feature of the present invention lies in the word linecontrol circuit 3. Namely, as will be described later in detail, theword line control circuit 3 consists of a row address decoder and a wordline driver. The word line control circuit 2 adopts a layout in whichthe row address decoder is arranged only at one side of the memory cellarray 1 and the word line drivers are arranged at both sides of thememory cell array 1, respectively.

In this case, a signal line for connecting the row address decoder atone side of the memory cell array 1 to the word line driver at the otherside thereof, is arranged on the memory cell array 1. The presentinvention improves the word line control circuit 3 so as to minimize theadverse effect of this signal line on the operations of memory cells.

The third feature of the present invention lies in the read operation.Namely, according to the present invention, the relationship betweenfour-level data and the threshold voltages of memory cells is set asshown in, for example, FIG. 20 (which detail will be described later).

In that case, even page data is read by two read operations (“READ01”and “READ00”) and odd page data is read by one read operation(“READ00”). That is, a total of three read operations allow reading thefour-level data, thereby making it possible to shorten read time (oraccelerate data read).

The fourth feature of the present invention lies in the programoperation (particularly, verification operation). Namely, according tothe present invention, the relationship between four-level data and thethreshold voltages of memory cells is set as shown in, for example, FIG.20 (which detail will be described later).

In that case, during the program operation of even page data, “11” and“10” are programmed into memory cells. Then, during the programoperation of odd page data, when odd page data is “0”, the “11” state ischanged to the “01” state and the “10” state is changed to the “00”state. Here, the change amount of the threshold voltages in case ofchanging the “11” state to the “01” state is larger than the changeamount of threshold voltages in case of changing the “10” state to the“00” state.

It is quite natural, therefore, that the “00”-programming is completedearlier than the “01”-programming. Thus, after completing the“00”-programming, “00” verify-read may be omitted and only “01”verify-read may be carried out. By doing so, it is possible to shortenprogram time (accelerate programming) for four-level data programming.

The fifth feature of the present invention lies in the fact that refreshoperation is carried out to the DRAM cell (capacitor) provided insteadof a latch circuit in the data circuit 2 during, for example, theprogram operation. Namely, according to the present invention, as shownin the first feature stated above, at least one of a plurality ofstorage circuits used to temporarily store multi-level data (n-leveldata) is changed to a DRAM cell (capacitor).

In this case, the area of the data circuit can be advantageouslyreduced. However, the charges of the capacitor gradually decrease due toleakage thereof. If the change of data due to leakage causes adisadvantage, refresh operation is required. In other words, during theprogram operation, a refresh sequence for the DRAM cell in the datacircuit 2 needs to be added to an ordinary program sequence.

The sixth feature of the present invention lies in the fact that a writecache is provided in the data circuit. In this case, if a programoperation is executed over a plurality of pages, for example, it ispossible to execute the program operation (the supply of a programpulse) and to input program data in parallel. This can dispense withdata load time for loading data on page 2 and the following pages,thereby making it possible to accelerate the program operation.

The seventh feature of the present invention lies in the fact thatrefresh operation is carried out to a DRAM cell if the write cacheprovided in the data circuit consists of the DRAM cell (capacitor) andthe change of data due to leakage causes a disadvantage.

The four-level NAND cell type EEPROM according to the present inventionas well as the first to second features stated above will be describedhereinafter in detail.

[Data Circuit] . . . First Feature

FIG. 9 shows one example of the data circuit 2 shown in FIG. 8. FIG. 10shows part of the memory cell array 1 shown in FIG. 9.

This example shows the data circuit for one column. Actually, one datacircuit is provided, for example, for each of a plurality of columns ofthe memory cell array 1. That is, the data circuit 2 shown in FIG. 8consists of a plurality of data circuits corresponding to the pluralcolumns of the memory cell array 1.

Further, in this embodiment, two bit lines BLe and BLo are arranged inone column and one data circuit is connected to these two bit lines BLeand BLo. The reasons the two bit lines BLe and BLo are connected to onedata circuit are to attain the following objects: (1) to prevent thegeneration of noise due to the capacitive coupling between adjacent bitlines during the read operation (to adopt a shield bit line readmethod); and (2) to intend to reduce the number of data circuits and tothereby decrease the chip area.

Additionally, in this embodiment, it is assumed that four-level data(two-bit data) are stored in one memory cell. Due to this, two storagecircuits are provided in one data circuit so as to temporarily store thefour-level data during the program/read operations.

Reference symbol LATCH1 denotes one of the two storage circuits, i.e., alatch circuit. The latch circuit LATCH1 consists of a flip-flop circuit(SRAM cell) consisting of clocked inverters CINV1 and CINV2. The latchcircuit LATCH1 is controlled by control signals SEN, SENB, LAT and LATB.

It is noted that signal “***B” indicates the inversion signal of asignal “***”. That is, the level of the signal “***B” and that of thesignal “***” are opposite in phase (when one level is “H”, the other is“L”). This definition applies to the following description.

Reference symbol DLN(C1) denotes a capacitor which is the other storagecircuit of the two storage circuits. This capacitor CLN(C1) consists ofa low voltage depletion N channel MOS transistor (MOS capacitor) appliedwith a voltage not higher than the power supply voltage Vcc. In thisembodiment, an N channel MOS transistor TN5 functions as a gate and datais latched by a node CAP1 ij. That is, the latch circuit consists of aDRAM cell consisting of the capacitor DLN(C1) and the MOS transistorTN5.

In FIG. 9, an MOS transistor to which symbol “HN** (* is number, symbolor the like) is added is a high voltage enhancement N channel MOStransistors having a threshold voltage of, for embodiment, about 0.6V. Ahigher voltage than the power supply voltage Vcc is applied to the MOStransistor. This MOS transistor is turned off when gate potential is 0V.

Also, an MOS transistor to which symbol “DLN**” is added is a lowvoltage depletion N channel MOS transistor having a threshold voltageof, for example, about −1V and applied with a voltage not higher thanthe power supply voltage Vcc. In this embodiment, this transistor isused as an MOS capacitor.

Further, an MOS transistor to which symbol “TN**” is added is a lowvoltage enhancement N channel MOS transistor having a threshold voltageof, for example, about 0.6V and applied with a voltage not higher thanthe power supply voltage Vcc. This transistor is turned off when gatepotential is 0V.

In case of the MOS transistors HN1 e, HN1 o, HN2 e and HN2 o, one of thetwo bit lines BLe and BLo is used as a bit line to which data is readand the other is used as a shield bit line.

That is, the potential of BLCRL is set at the ground potential Vss.Further, when the level of BIASo is “H” and that of BIASe is “L”, datais read to the bit line BLe and the bit line BLo becomes a shield bitline to prevent noise generated when reading the data to the bit lineBLe. On the other hand, when the level of BIASe is “H” and that of BIASois “L”, data is read to the bit line BLo and the bit line BLe becomes ashield bit line to prevent noise generated when reading the data to thebit line BLo.

An MOS transistor TN7 is a bit line precharge MOS transistor to presetone bit line, to which data is read, of the two bit lines BLe and BLoat, for example, the power supply potential Vcc. The MOS transistor TN7is controlled by a control signal BLPRE.

An MOS transistor TN9 is a clamping MOS transistor for controllingelectrical connection/disconnection between the bit lines BLe and BLoand the data circuit (important parts thereof). The MOS transistor TN9functions to precharge the bit lines BLe and BLo during, for example,the read operation and then keep the bit lines BLe and BLo in a floatingstate until the data read to the bit line BLe or BLo is sensed. The MOStransistor TN9 is controlled by a control signal BLCLMP.

The MOS transistors TN1, . . . , TN6, TN8 and TN10 are provided tocontrol odd/even page data during the program/read operations (orverification operation), and to detect whether or not the program/eraseoperations have been successfully completed for all the selected memorycells after verify-read (Program/Erase Completion detection) during theprogram/erase operations.

It is noted that an output signal COMi is used during the Program/Erasecompletion detection.

An MOS transistor TP1 is a preset transistor for presetting thepotential of a sense node DTNij at Vdd. The MOS transistor TP1 iscontrolled by a control signal nPRST.

The MOS transistor TN10 is an equalizer circuit equalizing thepotentials of the two output nodes Naij and Nbij of the latch circuitLATCH1. The MOS transistor TN10 is controlled by a control signal EQPB.

MOS transistors TN11 and TN12 function as column switches fordetermining electrical connection/disconnection between the nodes Naij,Nbij and input/output lines IOj and nIOj, respectively. When the levelof a column select signal CSLi is “H”, the MOS transistors TN11 and TN12are turned on and the output nodes Naij and Nbij of the latch circuitare electrically connected to the input/output lines IOj and nIOj,respectively.

The column select signal CSLi is outputted from the column decoder 4shown in FIG. 8. A column decoder is constituted by an NAND circuit asshown in FIG. 11. That is to say, for example, VAK1, CBK2, and CCH3 areall “H”, the column select signal CSLi becomes “L”.

In FIG. 9, reference symbol Vdd (e.g., about 2.3V) denotes a lowerinternal power supply potential than an external power supply potentialVcc. The internal power supply potential Vdd is generated from theexternal power supply potential Vcc. Alternatively, the external powersupply potential Vcc instead of the internal power supply potential Vddmay be applied to the data circuit.

[Batch Detection Circuit]

FIG. 12 shows important parts of the batch detection circuit 10 shown inFIG. 8.

The batch detection circuit 10 functions to detect whether or notprogram/erase operations have been successfully completed for allselected memory cells after verify-read (Program/Erase completiondetection).

Each data circuit has a constitution as shown in FIG. 9. REG2−k (k=0, 1,2, 3) is REG2 (see FIG. 9) in the (k+1)-th and (k+5)-th data circuits.

Output nodes COMi of the first to fourth data circuits are mutuallyconnected and the connection node COMi1 thereof is also connected to thegate of a P channel MOS transistor TP2. Likewise, output nodes COMi ofthe fifth to eighth data circuits are mutually connected and theconnection node CoMi2 thereof is also connected to the gate of a Pchannel MOS transistor TP3.

P channel MOS transistors TP13 and TP14 function to set the potentialsof nodes COMi1 and COMi2 at the internal power supply potential Vdd andthen turn the nodes COMi1 and COMi2 into a floating state during theProgram/Erase completion detection. The MOS transistors TN13 and TN14are controlled by a control signal COMHn.

An N channel MOS transistor TN15 functions to set the potential of anode NCOM at the ground potential Vss and then turn the node NCOM into afloating state. The MOS transistor TN15 is controlled by a controlsignal NCOML.

During the Program/Erase completion detection, the potential level ofthe output signal COMi (see FIG. 9) from the data circuit correspondingto the memory cell for which the program/erase operations have not beensufficiently completed, decreases from “H” to “L”. Accordingly, thelevel of the node NCOM is changed from “L” into “H” and the level of anode FLAG becomes “L”.

On the other hand, if the program/erase operations have beensufficiently completed for all the memory cells, the potential levels ofoutput signals COMi (see FIG. 9) from all data circuits remain “H”.Accordingly, the level of the node NCOM remains “L” and the level of thenode FLAG becomes “H”.

As can be seen from the above, by detecting the potential level of thenode FLAG, it is possible to detect whether or not the program/eraseoperations have been successfully completed for all the selected memorycells. The operation of the Program/Erase completion detection will bedescribed later in detail.

In this embodiment, the eight data circuits are grouped into one unitand the voltage level of the node FLAG is detected for eight columns ofmemory cells corresponding to these eight data circuits, therebydetecting whether or not the program/erase operations have beensufficiently completed.

The reason for grouping the eight data circuits into one unit is toreplace memory cells of a redundancy circuit in units of eight columnscorresponding to these eight data circuits. That is, when a fuse element(enclosed by a broken line) is cut off, the memory cells connected tothese eight data circuits always turn into an unselected state andauxiliary memory cells in a redundancy region are selected.

Accordingly, if the memory cells of the redundancy circuit are replacedin units of n columns corresponding to n data circuits (where n is anatural number), the n data circuits are grouped into one unit.

It is noted that the node FLAG is a common node to all columns. If thenumber of columns is, for example, 2048 and eight data circuits(columns) are set as a redundancy replacement unit, then 256 circuitsshown in FIG. 12 exist on a chip. These 256 circuits are connected tothe common node FLAG.

[Word Line Control Circuit] . . . Second Feature

FIG. 13 shows a concrete example of the word line control circuit shownin FIG. 8.

The memory cell array 1 consists of a plurality of memory cell blocksarranged in column direction. Each of the memory cell blocks has aplurality of NAND cell units arranged in row direction. The concreteexample of the memory cell array and the NAND cell units is shown inFIGS. 61 to 63.

In this embodiment, one row address decoder and one word line driver areprovided per memory cell block.

For example, word lines WL1, . . . WL16 and select gate lines SG1 andSG2 in the first memory cell block are connected to the first word linedriver RMAIN1. The first word line driver RMAIN1 receives the outputsignal (decoding result) of the first row address decoder RADD1 fordetermining whether to select/unselect the first memory cell block.

In this way, the word lines WL1, WL16 and the select gate lines SG1 andSG2 in the i-th memory cell block (where i=1, 2, . . . ) are connectedto the i-th word line driver RMAINi. The word line driver RMAINireceives the output signal (decoding result) of the i-th row addressdecoder RADDi for determining whether to select/unselect the i-th memorycell block.

In this embodiment, the word line drivers are arranged at both sides ofthe memory cell array 1 (two end portions thereof in row direction).

To be specific, the word line drivers RMAIN1, RMAIN3, . . .corresponding to the odd-numbered memory cell array blocks are arrangedat one side (left side) of the two end portions of the memory cell array1 in row direction, whereas the word line drivers RMAIN2, RMAIN4, . . .corresponding to the even-numbered memory cell array blocks are arrangedat the other side (right side) of the two end portions of the memorycell array 1 in row direction.

Such arrangement of the word line drivers RMAINi on both ends of thememory cell array 1 facilitates designing the word line drivers RMAIN1(or increases the degree of freedom in layout). That is to say, in thisembodiment, one word line driver can secure a layout space for twomemory cell blocks in column direction.

Furthermore, the word lines WL1, . . . WL16 and the select gate linesSG1 and SG2 in one memory cell block are always driven from one side (orthe other side) of the memory cell array 1 by the word line drivercorresponding to this memory cell block. This can, therefore, preventdrive signal supply timing for the memory cells and the selecttransistors in a predetermined NAND cell unit in the selected block fromshifting.

On the other hand, the row address decoders RADDi (where i=1, 2, . . . )are arranged only at one side of the two end portions of the memory cellarray 1 in row direction. This means that it suffices to arrange signallines (address buses) for applying row address signals to the rowaddress decoders RADDi only at one side of the memory cell array 1. Thearea of the address buses can be, therefore, reduced, resulting in acontribution to the reduction of the chip area.

Namely, if providing that the row address decoders RADDi are arranged onthe two end portions of the memory cell array 1 in row direction as inthe case of the word line drivers RAMINi, it is necessary to arrangeaddress buses on the two end portions of the memory cell array 1 in rowdirection. This is not advantageous for the reduction of the area of thememory cell array 1.

In this embodiment, as a result of arranging the row address decodersRADDi only on one of the two end portions (at one side of) the memorycell array 1 in row direction, signal lines 22 are arranged on thememory cell array 1. The signal lines 22 are used to apply the outputsignals (decoding results) of the row address decoders RADD2, RADD4, . .. corresponding to the even-numbered memory cell array blocks to theword line drivers RMAIN2, RMAIN4, . . . , respectively.

During normal operation, a signal RDECADS is transmitted through thissignal line 22. Accordingly, it is necessary to prevent the potential ofthe signal lines 22 from adversely affecting the memory cell operation.The present invention provides novel row address decoders RADDi and wordline drivers RMAINi which can prevent the potential of the signal lines22 from adversely affecting the memory cell operation, which will bedescribed later in detail.

The potential generating circuit 9A has a booster (charge-pumpingcircuit) and generates a program potential Vpp and a transfer potentialVpass used in the program operation. The potential generating circuit 9Ais connected to a switching circuit 9B. The switching circuit 9Bfunctions to allot potentials including the program potential Vpp, thetransfer potential Vpass, the internal power supply potential Vdd andthe ground potential Vss to signal lines CG1, . . . CG16 correspondingto the word lines WL1, . . . WL16.

The signal lines CG1, . . . CG16 are connected to the word line driversRMAINi. Namely, the signal lines CG1, . . . CG16 are connected to theword lines WL1, . . . WL16, respectively by way of potential transfertransistors HNt1, HNt2, . . . HNt16 (to be described later) in the wordline drivers RMAINi.

[Device Structure] . . . regarding signal lines 22 shown in FIG. 13

FIG. 14 is a cross-sectional view of an odd-numbered memory cell blockof FIG. 13 in column direction.

In case of odd-numbered memory cell blocks, the row address decodersRADD1, RADD3, . . . and the word line drivers RMAIN1, RMAIN3, . . . arearranged at one side of the memory cell array 1. Due to this, signallines connecting the row address decoders RADD1, RADD3, . . . with theword line drivers RAMIN1, RAMIN3, . . . are not arranged on the memorycell array 1.

The concrete structure of the memory cell block will be describedhereinafter.

A double-well region consisting of an n well region 11-2 and a p wellregion 11-3, is formed in a p silicon substrate 11-1. For example, 16memory cells M1, . . . M16 connected in series are formed on the p wellregion 11-3. Each memory cell consists of an N channel MOS transistorand has a stack gate structure consisting of a floating gate electrodeand a control gate electrode.

Select transistors S1 and S2 are connected to the two end portions ofthe serially-connected memory cells M1, . . . M16, respectively. Each ofthe select transistors S1 and S2 consists of an N channel MOStransistor. The diffused layer (drain) 24 of the bit line-side selecttransistor S1 is connected to a metal wiring B in the first wiring layerM0. The diffused layer (source) 25 of the source line-side-selecttransistor S2 is connected to a source line SL in the first wiring layerM0.

The gate electrode (select gate line (polysilicon)) of the selecttransistor S1 is connected to the metal wiring SG1 in the first wiringlayer M0 to decrease the wiring resistance of the select gate line.Contact portions between the select gate line (polysilicon) and themetal wiring SG1 are provided at positions, for example, at which theselect gate line intersect 528 bit lines, respectively.

Likewise, the gate electrode (select gate line (polysilicon)) of theselect transistor S2 is connected to the a metal wiring SG2 in the firstwiring layer M0. Contact portions between the select gate line(polysilicon) and the metal wiring SG2 are provided at positions, forexample, at which the select gate line intersect 528 bit lines,respectively.

The bit lines BL is arranged in the second wiring layer M1 provided onthe first wiring layer M0. The bit line BL extends in column directionand is connected to the diffused layer (drain) 24 of the selecttransistor S1 through the metal wiring B in the first wiring layer M0.

The respective signal lines in the first and second wiring layers M0 andM1 are made or, for example, aluminum, copper or an alloy thereof.

A row shield line 23 is arranged above the memory cells M1, . . . M16and between the metal wirings SG1 and SG2.

The row shield line 23 is arranged so as to prevent the generation ofso-called coupling noise during the program/read operations and tosufficiently increase the potentials of unselected word lines during theerase operation. The potential of the row shield line 23 is normally setat the same as that of the double-well region (cell well) 11-2 and 11-3.

During the program/read operations, the cell well potential is normallyset at the ground potential Vss. At this moment, therefore, thepotential of the row shield line 23 is fixed to the ground potentialVss, as well. In that case, since the coupling capacity between the bitline BL and the word line WL is almost eliminated, it is possible toprevent coupling noise from occurring to the data transmitted throughthe bit line.

Further, during the program/read operations, the potentials of theselect gate lines (metal wirings) SG1 and SG2 in unselected blocks areset at the ground potential Vss. Due to this, the select gate lines(metal wirings) SG1 and SG2 also function as shield lines during theprogram/read operations.

In this way, by setting the potentials of the row shield line 23 and theselect gate lines (metal wirings) SG1 and SG2 in the unselected blocksat the ground potential Vss, respectively, it is possible to reduce thecapacitive coupling between the bit line BL and the word line WL and toprevent coupling noise from being applied to the data transmittedthrough the bit line.

Meanwhile, during the erase operation, the potential of the row shieldline 23 is set at an erase potential Vera (e.g., about 20V). This isbecause the potentials of the word lines WL in unselected blocks are tobe sufficiently increased during the erase operation.

Namely, during the erase operation, the word lines (control gate lines)WL of unselected blocks are in a floating state. When the erasepotential (e.g., about 20V) is applied to the double-well region (cellwell) 11-2, 11-3, the potentials of the word lines WL in the unselectedblocks are increased by capacitive coupling.

Therefore, if the potential of the row shield line 23 is set at theerase potential Vera during the erase operation, the potential of theword line WL is not influenced by the potential of the row shield line23 when the potential of the cell wells 11-2 and 11-3 rises from theground potential Vss to the erase potential Vera. Thus, it is possibleto sufficiently increase the potentials of the word lines WL in theunselected blocks to the same level as that of the erase potential Vera.

Further, the potentials of the word lines WL in the unselected blocksrise sufficiently to the same level as that of the erase potential Vera.Due to this, a high electric field is not applied to the tunnel oxidefilm between the floating gate electrode and the cell wells anderroneous data erase can be, therefore, prevented.

At this moment, providing that the potential of the row shield line 23is the ground potential Vss or the power supply potential Vcc, thepotential of the word line WL is influenced by the potential of the rowshield line 23 (Vss or Vcc) and does not rise to the same level as thatof the erase potential Vera. Accordingly, a high electric field maypossibly be applied to the tunnel oxide films of the unselected memorycells to thereby cause erroneous data erase.

FIG. 15 is a cross-sectional view of an even-numbered memory cell blockof FIG. 13 in column direction.

In case of even-numbered memory cell blocks, the row address decodersRADD2, RADD4, . . . are arranged on one end of the memory cell array 1in row direction. The word line drivers RMAIN2, RMAIN4, . . . arearranged on the other end of the memory cell array 1 in row direction.Accordingly, signal lines 22 connecting the row address decoders RADD2,RADD4, . . . with the word line drivers RMAIN2, RMAIN4, . . . ,respectively, are arranged on the memory cell array 1.

The concrete structure of the memory cell block in FIG. 15 will bedescribed hereinafter.

A double-well region consisting of an n well region 11-2 and a p wellregion 11-3, is formed in a p silicon substrate 11-1. For example, 16memory cells M1, . . . M16 connected in series are formed on the p wellregion 11-3. Each memory cell consists of an N channel MOS transistorand has a stack gate structure consisting of a floating gate electrodeand a control gate electrode.

Select transistors S1 and S2 are connected to the two end portions ofthe serially connected memory cells M1, . . . M16, respectively. Each ofthe select transistors S1 and S2 consists of an N channel MOStransistor. For example, the diffused layer (drain) 24 of the bitline-side select transistor S1 is connected to a metal wiring B in thefirst wiring layer M0. The diffused layer (source) 25 of the sourceline-side select transistor S2 is connected to a source line SL in thefirst wiring layer M0.

The gate electrode (select gate line (polysilicon)) of the selecttransistor S1 is connected to the metal wiring SG1 in the first wiringlayer M0 to decrease the wiring resistance of the select gate line.Contact portions between the select gate line (polysilicon) and themetal wiring SG1 are provided at positions, for example, at which theselect gate line intersect 528 bit lines, respectively.

Likewise, the gate electrode (select gate line (polysilicon)) of theselect transistor S2 is connected to the metal wiring SG2 in the firstwiring layer M0 to decrease the wiring resistance of the select gateline. Contact portions between the select gate line (polysilicon) andthe metal wiring SG2 are provided at positions, for example, at whichthe select gate line intersect the 528 bit lines, respectively.

The bit lines BL is arranged in the second wiring layer M1 provided onthe first wiring layer M0. The bit line BL extends in column directionand is connected to the diffused layer (drain) 24 of the selecttransistor S1 through the metal wiring B in the first wiring layer M0.

The respective signal lines in the first and second wiring layers M0 andM1 are made of, for example, aluminum, copper or an alloy thereof.

A signal line 22 is arranged above the memory cells M1, . . . M16 andbetween the metal wirings SG1 and SG2.

The device of the even-numbered memory cell block is characterized inthat the signal line 22 is provided instead of the row shield line 23(see, FIG. 14) of the odd-numbered memory cell block.

As described with reference to FIG. 13, the signal line 22 functions totransmit the output signal RDECAD of the row address decoder to the wordline driver. Accordingly, the potential of the signal line 22 cannot beset at the same as that of the row shield line 23.

The present invention proposes a word line control circuit capable ofsetting the potential of the signal line 22 at an appropriate valueaccording to an operation mode, preventing so-called coupling noiseduring the program/read operations and sufficiently increasing thepotentials of unselected word lines during the erase operation withouthampering the functions of the above-stated signal line 22.

Now, an embodiment of the word line control circuit of the presentinvention will be described. Then, description will be given to how thepotential level of the signal line 22 varies in each operation mode ifthis circuit is used.

[Example of Word Line Control Circuit]

First, symbols added in the drawings are defined as follows.

An MOS transistor to which symbol “HN** (where * is a number, symbol orthe like)” is added is a high voltage enhancement N channel transistorhaving a threshold voltage of, for example, about 0.6V and is appliedwith a higher voltage than the power supply voltage Vcc. This transistoris turned off when gate potential is 0V.

An MOS transistor to which symbol “1HN** (where * is a number, symbol orthe like)” is added is a high voltage enhancement N channel MOStransistor having a threshold voltage of, for example, about 0.1V and isapplied with a higher voltage than the power supply voltage Vcc.

An MOS transistor to which symbol “DHN**” is added is a high voltagedepletion N channel MOS transistor having a threshold voltage of, forexample, about −1V. If the potentials of the gate and drain of thetransistor are set at the power supply potential Vcc, the potential ofthe drain Vcc is transferred to the source thereof. In addition, if thepotential of the gate is set at 0V while the potentials of the sourceand drain are Vcc, this transistor is turned off.

An MOS transistor to which symbol “TN**” is added is a low voltageenhancement N channel MOS transistor having a threshold voltage of, forexample, about 0.6V and is applied with a voltage of not higher than thepower supply voltage Vcc. An MOS transistor to which symbol “TP**” isadded is a low voltage enhancement P channel MOS transistor having athreshold voltage of, for example, about 0.6V.

FIG. 16 shows the important parts of the row address decoder provided tocorrespond to the odd-numbered memory cell block.

To be exact, this row address decoder RADD1 functions as a blockdecoder. Namely, when the first memory block is selected, for example,the levels of all row address signals AROWi, . . . AROWj become “H” andthe level of an output signal RDECAD becomes “H”. The operation of therow address decoder RADD1 will be described later in detail.

FIG. 17 shows the important parts of the word line driver provided tocorrespond to the odd-numbered memory cell block.

The main constituent elements of the word line driver RMAIN1 are a highvoltage switching circuit 26 and transfer MOS transistors HN5, HN6,HNt1, . . . HNt16.

The high voltage switching circuit 26 comprises the first booster unitconsisting of an MOS capacitor DHN4 and an MOS transistor 1HN1, and thesecond booster unit consisting of an MOS capacitor DHN5 and an MOStransistor IHN2.

The gate of the MOS transistor HN3 is connected to a connection node Bconnecting the MOS transistors IHN1 and IHN2. In this case, thepotentials of nodes A, B and transferG1 gradually increase synchronouslywith a clock signal Owc while the potential levels of the gate and thesource of the MOS are maintained to be opposite in phase. Thus, boostingefficiency improves.

The high voltage switching circuit 26 turns into an operation state whenthe level of the output signal RDECAD of the row address decoder RADD1is “H”. Namely, when the level of the output signal RDECAD is “H”, theoutput signal of an NAND circuit NAND1 becomes a clock signal oppositein phase to the clock signal Owc. The output signal of the NAND circuitNAND1 is applied to one end of each of the MOS capacitors DHN4 and DHN5.

As a result, a boosting potential is applied to the gates of thetransfer MOS transistors HN5, HN6, HNt1, . . . HNt16, respectively andthe transfer MOS transistors HN5, HN6, HNt1, . . . HNt16 are turned on.

If the level of the output signal RDECAD of the row address decoderRADD1 is “H”, MOS transistors HN7 and HN8 are turned off. At thismoment, the potentials of the signal lines SGD and SGS become theinternal power supply potential Vdd and applied to the select gate linesSG1 and SG2 through the transfer MOS transistors HN5 and HN6,respectively.

Further, the potentials of the signal lines CG1, CG2, . . . CG16 are setpredetermined potentials according to an operation mode by the switchingcircuit 9B (see FIG. 8). The potentials of the signal lines CG1, CG2, .. . CG16 are applied to the word lines WL1, WL2, . . . WL16 through thetransfer MOS transistors HNt1, . . . HNt16, respectively.

FIG. 18 shows the important parts of the row address decoder provided tocorrespond to the even-numbered memory cell block.

The row address decoder RADD2 includes the same circuit as that of therow address decoder RADD1 shown in FIG. 16. Namely, a circuit enclosedby a broken line X1 is the same as the row address decoder RADD1. It isnoted that the same constituent elements shown in FIG. 18 as those inFIG. 16 are denoted by the same reference symbols.

The row address decoder RADD2 of the present invention is characterizedby newly providing an inverter I4, clocked inverters CINV3 and CINV4 anddepletion high voltage N channel MOS transistors DHN6 and DHN7.

The clocked inverter CINV4 functions to turn the potential of the outputsignal RDECADS of the row address decoder corresponding to the selectedmemory cell block (the potential of the signal line 22 shown in FIG. 8)into the ground potential Vss during the erase operation (ERASE) and toturn the output signals RDECADS of the row address decoderscorresponding to the unselected memory cell block into the internalpower supply potential Vdd.

The MOS transistor DHN6 functions to turn the signal line 22 (see FIG.15) into a floating state together with a transistor DHN9 shown in FIG.19 to be described later.

During the erase operation (ERASE), the level of signal RDECADS1 becomes“H (Vdd)” in the selected memory block, and becomes “L (Vss)” in theunselected memory cell block.

Providing that, as in the case of the conventional decoder, this signalRDECADS1 is applied to the signal line 22 (see FIG. 15) on the memorycell array, the level of the signal line 22 (see FIG. 15) on the memorycell array becomes “L (Vss)” in the unselected memory cell block.

In that case, if the erase potential Vera is applied to the cell wellsby the capacitive coupling between the cell wells and the word line andthe potential of the word lines in the unselected memory cell block isto be increased, the potential of the word line does not sufficientlyrise due to the influence of the signal line 22 (FIG. 15) having theground potential Vss.

Since the present invention newly provides a clocked inverter CINV4, thelevel of the output signal RDECADS becomes “L (Vss)” in the selectedmemory cell block and becomes “H (Vdd)” in the unselected memory cellblock during the erase operation (ERASE).

That is to say, the level of the signal line 22 (see FIG. 15) on thememory cell array in the unselected memory cell block become “H (Vdd)”and into a floating state by the cutoff of the MOS transistors DHN6 andDHN9 (FIG. 19).

Accordingly, in case of increasing the potential of the word lines inthe unselected memory cell blocks by the capacitive coupling between thecell wells and the word line, the potential of the word linesufficiently rises with less influence of the signal line 22 (FIG. 15)having the internal power supply potential Vdd.

FIG. 19 shows the important parts of the word driver provided tocorrespond to the even-numbered memory cell block.

Among the main constituent elements of the word line driver RMAIN2, thehigh voltage switching circuit 26 and the transfer MOS transistors HN5,HN6, HNt1, . . . HNt16 are the same as those in the word line driverRMAIN2 shown in FIG. 17. Namely, a circuit enclosed by a broken line X2is almost the same as the row address decoder RADD1 of FIG. 17. It isnoted that the same constituent elements in FIG. 19 as those in FIG. 17are denoted by the same reference symbols.

The word line driver RMAIN2 of the present invention is characterized bynewly providing clocked inverters CINV5, CINV6 and CINV7, depletion highvoltage N channel MOS transistors DHN8 and DNH9 and enhancement Pchannel MOS transistors TP6 and TP7.

The clocked inverter CINV7 functions to return the potential of theoutput signal RDECADS (the potential of the signal line 22 of FIG. 5) ofthe row address decoder corresponding to the selected memory cell blockfrom the ground potential Vss to the internal power supply potentialVdd, return the potential of the output signal RDECADS of the rowaddress decoder corresponding to the unselected memory cell block fromthe internal power supply potential Vdd to the ground potential Vssduring the erase operation (ERASE), and then to apply the signals as asignal RDECADS2 to the circuit enclosed by the broken line X2.

The MOS transistor DHN9 functions to turn, together with the transistorDHN6 shown in FIG. 18, the signal line 22 (see FIG. 15) into a floatingstate.

In this way, the inverter I4, the clocked inverters CINV3 and CINV4, thedepletion high voltage N channel MOS transistors DHN6 and DHN7 in therow address decoder RADD2 shown in FIG. 18 attain the same object asthat of the clocked inverters CINV5, CINV6 and CINV7, the depletion highvoltage N channel MOS transistors DHN8 and DHN9 and the enhancement Pchannel MOS transistors TP6 and TP7 in the word line driver RMAIN2 shownin FIG. 19. Thus, they are used in pairs.

It is noted that FIGS. 16 to 19 show that the potential Vdd (theinternal power supply potential lower than the external power supplypotential) is applied to those circuits as a power supply potential.Alternatively, the external power supply potential Vcc instead of theinternal power supply potential Vdd may be applied to these circuits.

[Potential Level of Signal Line 22]

Next, description will be given to how the potential level of the signalline 22 (see FIG. 15) changes in each operation mode. It is noted thatonly the potential level of the signal line 22 will be described hereinand that the operation of the word line control circuit including thepotential level of the signal line 22 will be described later in detail.

In this embodiment, the signal line 22 (FIG. 15) connects the rowaddress decoder (FIG. 18) with the word line driver (FIG. 19)corresponding to the even-numbered memory cell block. Accordingly, whilereferring to FIGS. 18 and 19, the potential level of the word linedriver select signal RDECADS transmitted through the signal line 22(FIG. 15) will be described.

The potential level of the output signal RDECADS of the row addressdecoder RADD2 differs among the operation modes.

In operations other than the erase operation (ERASE) (Program/Read,Verify-Read operations), the potentials of ROWERASE1B, ROWPROG1,ROWERASE2B, ROWERASE3 n and ROWGATE are set at the power supplypotential Vdd (the internal potential lower than the external powersupply potential Vcc, or the external power supply potential Vcc), andthe potentials of ROWERASE1, ROWPROG1B and ROWERASE2 are set at theground potential Vss, respectively.

At this time, the clocked inverters CINV3, CINV5 and CINV6 turn into anoperation state and the clocked inverters CINV4 and CINV7 turn into annon-operation state. Also, the MOS transistor TP6 is turned off.

In the selected memory cell block, the level of the output signalRDECADS1 from the portion enclosed by the broken line X1 becomes “H”,i.e., the internal power supply potential Vdd and the level of theoutput signal RDECADS from the row address decoder RADD2 also becomes“H”, i.e., the internal power supply potential Vdd.

In the unselected memory cell block, on the other hand, the level of theoutput signal R from the portion enclosed by the broken line X1 becomes“L”, i.e., the ground potential Vss and the level of the output signalRDECADS from the row address decoder RADD2 also becomes “L”, i.e., theinternal power supply potential Vss.

Accordingly, in operations other than the erase operation, the potentialof the signal line 22 (see FIG. 15), arranged on the memory cell arrayin the unselected memory cell blocks becomes the ground potential Vss,and the potentials of the select gate lines SG1 and SG2 in theunselected memory cell block become the ground potential Vss, as well.These signal lines 22, SG1 and SG2 function as shield lines between thebit line and the word line (as in the case of the row shield line 23shown in FIG. 14). As a result, it is possible to reduce coupling noiseoccurring to the data transmitted through the bit lines.

In the erase operation, the potentials of ROWERASE1B, ROWPROG1,ROWERASE2B, ROWERASE3 n and ROWGATE are set at the ground potential Vss,and the potentials of ROWERASE1, ROWPROG1B and ROWERASE2 are set at theinternal power supply potential Vdd (or the power supply potential Vcc),respectively.

At this time, the clocked inverters CINV4 and CINV7 turn into anoperation state and the clocked inverters CINV3, CINV5 and CINV 6 turninto a non-operation state. Also, the MOS transistor TP6 is turned on.

In the selected memory cell block, the level of the output signalRDECADS1 from the portion enclosed by the broken line X1 becomes “H”,i.e., the internal power supply potential Vdd, and the level of theoutput signal RDECADS from the row address decoder RADD2 becomes “L”,i.e., the ground potential Vss.

In the unselected memory cell block, the level of the output signalRDECADS1 from the portion enclosed by the broken line X1 becomes “L”,i.e., the ground potential Vss, and the level of the output signalRDECADS from the row address decoder RADD2 becomes “H”, i.e., theinternal power supply potential Vdd.

Further, ROWGATE has the ground potential Vss. Due to this, if thepotential of the signal line 22 (see FIG. 15) arranged on the memorycell array in the unselected memory cell block (potential of RDECADS)becomes about 1 to 1.5V, the MOS transistors DHN6 and DHN9 are cut offand thereby become a floating state.

In this way, in the erase operation, the potential of the signal line 22(see FIG. 15) arranged on the memory cell array in the unselected memorycell block is 1 to 1.5V and in a floating state. Namely, if the cellwells are applied with the erase potential Vera, the potential of thesignal line 22 (FIG. 15) rises by the capacitive coupling as in the caseof the word line. Thus, the signal line 22 (FIG. 15) does not suppressthe increase of the potential of the word line.

Accordingly, if the cell wells are applied with the erase potentialVera, the potentials of the word line in the unselected memory cellblocks advantageously, easily rises by the capacitive coupling betweenthe cell wells and the word line.

Following this, a high electric field is not applied to the tunnel oxidefilm of the memory cells in the unselected memory cell block, so that itis possible to prevent erroneous erase from occurring to the unselectedmemory cell block.

In the meantime, the fuse element in the broken line X in FIG. 18 (aswell as the fuse element in FIG. 16) is not cut off if a memory cellblock corresponding to this fuse element (row address decoder) is usedas an ordinary memory region for a user.

However, if the memory cell block corresponding to the fuse element (rowaddress decoder) is used as an ROM BLOCK region for storing device code,the fuse element is cut off and a user is inhibited from freelyconducting program/erase operations to the ROM BLOCK region.

The ROM BLOCK region has the following significance.

In the recent years, NAND type flash memories have been used as memoriesfor various types of electronic equipment. However, there are caseswhere NAND type flash memories are used as memories for data related tocopyrights such as those for storing music information by telephonecommunications.

To prevent illegal duplication, a chip number, i.e., a device code isstored in an NAND type flash memory.

The device code is characteristic of an individual NAND type flashmemory. If a user can freely reprogram this device code, the originalpurpose of the device code cannot be fulfilled.

Considering this, the device code is programmed into the ROM BLOCKregion of the NAND type flash memory before shipment and a user isinhibited from programming/erasing the ROM BLOCK region. Namely, a fuseelement is cut off in a memory cell block which becomes the ROM BLOCKregion.

By doing so, if music information is to be duplicated in, for example,an information reception-side NAND type flash memory from an informationproviding-side NAND type flash memory or the device code is to be readfrom the information providing-side NAND type flash memory and thedevice code of the information reception-side NAND type flash memorydiffers from that of the information providing-side NAND type flashmemory, then duplication is inhibited.

The fuse element is cut off right after the device code is programmedinto the memory cell block which becomes the ROM BLOCK region.

This is because if a pre-shipment test is conducted in a state in whichthe fuse element is not cut off, the device code is erased in this test.

Specifically, in the pre-shipment test, all blocks are simultaneouslyselected and programmed/erased to shorten test time. In other words,since the levels of all row address signals AROWi, . . . AROWj become“H”, the level of REDECADS1 becomes “H” (in FIG. 16, the level of RDECADbecomes “H”) if the fuse element is not cut off even with the level ofCMD ROMBA being “L”. As a result, the memory cell block which becomesthe ROM BLOCK region is selected.

On the other hand, even if the levels of all row address signals AROWi,. . . AROWj are “H”, the level of CMD ROMBA is “L” as long as the fuseelement is cut off. Thus, the level of RDECADS1 becomes “L” (in FIG. 16,the level of RDECAD becomes “L”) and the memory cell block which becomesthe ROM BLOCK region is not selected.

Even if the fuse element is cut off, it is necessary to read the devicecode stored in the ROM BLOCK region.

The data can be read from the ROM BLOCK region by setting the level ofCMD ROMBA at “H”. That is to say, if the level of CMD ROMBA becomes “H”and those of the signals AROWi, . . . AROWj in the ROM BLOCK regionbecome “H”, then the memory cell block which becomes the ROM BLOCKregion is selected.

Furthermore, even after the fuse element is cut off, the data in the ROMBLOCK region can be reprogrammed by inputting a special command tothereby set the levels of the CMD ROMBA and the signals AROWi, . . .AROWj in the ROM BLOCK region at “H”. In that case, a command to set thelevel of CMD ROMBA at “H” is made closed to ordinary users so as toprevent the data in the ROM BLOCK region from being illegallyreprogrammed.

In this embodiment, description has been given to a case of cutting thefuse element in the ROM BLOCK region. The fuse in FIG. 16 and that inthe broken line X of FIG. 18 are also cut off if a memory cell block isa defective block. In that case, the defective block is replaced by abackup block by a redundancy circuit.

[Description of Basic Operation] . . . Third to Fifth Features

Now, detailed description will be given to the operations of theimportant parts of the four-level NAND cell type EEPROM (FIG. 8) of thepresent invention in the respective operation modes such as a read mode,a program mode, an erase mode and a test (burn-in) mode. To be specific,the operations of the data circuit (FIG. 9), the batch detection circuit(FIG. 12) and the word line control circuit (FIGS. 13, and 16 to 19)will be described.

Before the description of the operations, one example of the thresholdvoltages of memory cells and a data programming method will be describedbriefly.

FIG. 20 is a distribution view of the threshold voltages (Vth) of memorycells in the four-level NAND cell type EEPROM.

Four-level data (two-bit data) are stored in one memory cell. In thisembodiment, as already described above, it is assumed that thefour-level data includes “11”, “10”, “00” and “01”. It is also assumedthat the four-level data (“11”, “10”, “00” and “01”) and the thresholdvoltages of memory cells has a relationship shown in FIG. 20.

That is, it is assumed that “11” is an erase state. A memory cell in theerase state has a negative threshold voltage Vth. It is also assumedthat “10”, “00” and “01” are program states. A memory cell in theprogram state has a positive threshold voltage Vth. Further, among theprogram states, the “10” state has the lowest threshold voltage, the“01” state has the highest threshold voltage and the “00” state has athreshold voltage between the threshold of the state “10” and that ofthe state “01”.

The four-level data (two-bit data) consists of even page data and oddpage data, and is programmed into a memory cell by two programoperations.

First, the even page data is programmed.

It is now assumed that all memory cells are in the erase state, i.e., inthe data “11” state. Thereafter, as shown in FIG. 21, when the even pagedata is programmed, the distribution of the threshold voltages Vth ofthe memory cells is divided into two sections according to the values(“1” and “0”) of the even page data.

That is to say, if the even page data is “1”, the tunnel oxide film ofeach memory cell is prevented from being applied with a high electricfield and the threshold voltage Vth of the memory cell is prevented fromrising. As a result, the memory cell is maintained in the erase state(“11” state) (program of even page data “1”).

On the other hand, if the even page data is “0”, then a high electricfield is applied to the tunnel oxide film of each memory cell, electronsare injected into the floating gate electrode of the memory cell and thethreshold voltage Vth of the memory cell rises by a predeterminedamount. As a result, the memory cell turns into a program state (“10”state) (program of even page data “0”).

The program of odd page data follows.

The odd page data is programmed based on program data (i.e., odd pagedata) inputted externally of a memory chip and on the even page dataalready programmed into the memory cell.

Namely, as shown in FIG. 22, if odd page data is “1”, the tunnel oxidefilm of each memory cell is prevented from being applied with a highelectric field and the threshold voltage Vth of the memory cell isprevented from rising. As a result, the memory cell in the “11” state(erase state) remains the “11” state and the memory cell in the “10”state turns into the “00” state (program of odd page data “0”).

On the other hand, if odd page data is “0”, the tunnel oxide film ofeach memory cell is applied with a high electric field and the thresholdvoltage Vth of the memory cell is increased by injecting electrons intothe floating gate electrode. As a result, the memory cell in the “11”state (erase state) turned into the “01” state and the memory cell inthe “10” state turns into the “00” state (program of odd page data “0”).

That is to say, in this embodiment, if the even page data is “1” and theodd page data is “1”, data “11” is programmed into each memory cell. Ifthe odd page data is “0” and the even page data is “1”, data “10” isprogrammed into the memory cell. If the even page data is “1” and theodd page data is “0”, data “01” is programmed into the memory cell. Ifthe even page data is “0” and the odd page data is “0”, data “00” isprogrammed into the memory cell.

In this way, by conducting two program operations, the distribution ofthe threshold voltages Vth of memory cells is divided into four section(“11”, “10”, “00” and “01”).

The present invention is characterized by a program method when odd pagedata is “0” (the fourth feature). To be specific, in this embodiment,four-level data and the threshold voltages of the memory cells is set tohave the relationship shown in FIG. 20. Due to this, if the odd pagedata is “0”, the “11” state is changed to the “01” state and the “10”state is changed to the “00” state (see FIG. 22).

Now, as is obvious from FIG. 22, the change amount of the thresholdvoltages if the state “11” is changed to the state “01” is larger thanthat if the state “10” is changed to the state “00”. In other words,since a program pulse is applied to a memory cell to which“00”-programming is conducted and to a memory cell to which“01”-programming is conducted on the same conditions, “00”-programmingis completed earlier than “01”-programming.

Utilizing this, the present invention (fourth feature) omits “00”verify-read after the completion of “00”-programming and then conductsonly the “01” verify-read to thereby shorten program time (accelerateprogram) (which will be described later).

Further, since the above-stated program method is adopted, the presentinvention is also characterized by verification-related circuits (e.g.,MOS transistor TN1, . . . TN6, TN8, TN10 and the like) in the datacircuit (FIG. 9).

Additionally, in this embodiment, since the four-level data and thethreshold voltages of the memory cells is set to have the relationshipshown in FIG. 20, the present invention is characterized by a data readmethod (the third feature).

According to prior art (Japanese Patent Application No. 8-98627), forexample, the “00” state and the “01” state are opposite to each otherwith regard to the relationship shown in FIG. 20. That is, the changeamount of the threshold voltages in a case where the state “11” ischanged to the state “01” and that in a case where the state “10” ischanged to the state “00” are almost the same.

Now, operations will be described concretely while referring to anoperation timing view.

1. Read Operation

Read operation consists of an even page data read operation and an oddpage data read operation.

1.-1 Even Page Data Read Operation

As is evident from FIG. 20, the “11” state and the “01” state are evenpage data “1” and the “10” state and the “00” state are odd page data“0”. That is, it is possible to judge whether the even page data is “1”or “0” from two read operations of “READ01” and “READ10”.

Accordingly, the even page data read operation consists of two readoperations of “READ01” and “READ10”. First, the “READ01” operation iscarried out and then the “READ10” operation follows.

1.-1.-1 “READ01”

FIG. 23 shows the “READ01” operation.

In the “READ01” operation, a read potential (the potential of a selectedword line) is set at Vcgr01 (e.g., about 1.45V) and it is recognizedwhether memory cell data is “01” or other data “11”, “10” or “00”.

First, in the row address decoder (FIGS. 16 and 18), the level of RDECPBis set at “L”. At this moment, the levels of both RDECAD (FIG. 16) andRDECADS1 (FIG. 18) are “L (Vss)” and all memory cell blocks are in anunselected state.

Thereafter, the level of RDECPB is changed from “L” to “H”. At thistime, the MOS transistor TP4 is turned off and the MOS transistor TN21is turned on (FIGS. 16 and 18).

Further, in a selected memory cell block, the levels of all row addresssignals AROWi, . . . AROWj become “H” and the levels of both RDECAD(FIG. 16) and RDECADS1 (FIG. 18) become “H”. In unselected memory cellblocks, since the level of at least one of the row address signalsAROWi, . . . AROWj is “L”, the levels of RDECAD (FIG. 16) and RDECADS1(FIG. 18) are maintained “L”.

In the word line driver (FIGS. 17 and 19) in the selected memory cellblock, the levels of the input signals RDECAD and RDECADS1 become “H”.Due to this, the high voltage switching circuit (NMOS charge-pumpingcircuit) 26 is actuated by an oscillation signal (clock signal) Owc.

Accordingly, in the word line driver (FIGS. 17 and 19) in the selectedmemory cell block, potential VRDEC is transferred to the output node ofthe high voltage switching circuit 26.

If the word line driver RMAIN1 (FIG. 17) in the first memory cell blockis selected, for example, the potential VRDEC (e.g., about 6V) isapplied to the output node TransferG1. If the word line driver RMAIN2(FIG. 19) in the second memory cell block is selected, for example, thepotential VRDEC (e.g., about 6V) is applied to the output nodeTransferG2.

As a result, the potentials of the gates of the transfer transistorsHNt1, HNt2, . . . HNt16 become VRDEC, and the potentials of the signallines CG1, CG2, . . . CG16 are transferred to the word lines (controlgate lines) WL1, WL2, . . . WL16 through the transfer transistors HNt1,HNt2, . . . HNt16, respectively.

The potentials of the signal lines SGD and SGS are also transferred tothe select gate lines SG1 and SG2 through the transfer transistors HN5and HN6, respectively.

Here, among the signal lines CG1, CG2, . . . CG16, the potential of aselected signal line is set at Vcgr01 (e.g., about 1.45V) by theswitching circuit (FIG. 8), whereas the potentials of the remainingunselected signal lines are set at Vread (e.g., about 3.5V) by theswitching circuit (FIG. 8).

Further, the potentials of the signal lines SGD and SDS are set at Vread(e.g., about 3.5V).

On the other hand, in each word line driver (FIGS. 17 and 19) in theunselected memory cell blocks, the potentials of RDECAD and RDECADS2 aretransferred to the output nodes TrasferG1 and TransferG2 of the highvoltage switching circuit 26, respectively.

That is, in each word line driver (FIGS. 17 and 19) in the unselectedmemory cell blocks, the potentials of both of the output nodesTransferG1 and TransferG2 become the ground potential Vss.

As a result, the transfer transistors HNt1, HNt2, . . . HNt16 are turnedoff and the word lines (control gate lines) WL1, WL2, . . . WL16 turninto a floating state. Further, the select gate lines SG1 and SG2 aregrounded by the signal lines SGS and SGD, respectively.

Operation timing shown in FIG. 23 will be described in detail.

It is assumed that a memory cell connected to the bit line BLe isselected and that the bit line BL0 is a shield bit line.

At the row side (word line control circuit side), first, at periodRCLK1, the level of BSTON becomes “H”. At this time, in the selectedmemory cell block, Vdd (RDECAD or RDECADS2) is transferred to the outputnode (TransferG1 or TransferG2) of the high voltage switching circuit inthe word line driver.

At period RCLK2, the level of BSTON becomes “L” and at period RCLK3, thepotential of HRDEC becomes VsgHH. Due to this, in the selected memoryblock, the potential of the output node (TransferG1 or TransferG2) ofthe high voltage switching circuit in the word line driver rises toVsgHH.

The potential of the selected word line CGselect is set at Vcgr01 (e.g.,about 1.45V) and those of unselected word lines CGunselect and thepotential SGD of the select gate line SG1 are set at Vread (e.g., about3.5V).

At the column side (data circuit side), at period RCLK2, the potentialof BLPRE becomes Vdd (e.g., about 2.3V). At period RCLK3, the potentialof BIASe becomes the ground potential Vss, and the potential of BIASobecomes Vsghh. At period RCLK4, when the potential of BLSe becomesVsghh, the bit line BLe is precharged and the potential of the bit lineBLo becomes the ground potential Vss.

The potential of BLCLMP while precharging the bit line BLe is Vclmp(e.g., about 2V). Due to this, after rising to about 0.8V, the bit lineBLe turns into a floating state. Then, at period RCLK7, the precharge ofthe bit line BLe is completed.

At period RCLK7, when the potential SGS of the select gate line SG2 isset at Vread, the potential of the bit line BLe decreases or ismaintained according to the data of the selected memory cell.

That is to say, if the selected memory cell data is “11”, “10” or “00”,this selected memory cell is turned on by the potential Vcgr01. Thus,the charges of the bit line BLe are discharged and the potential of thebit line BLe decreases to 0.3V or lower (while unselected memory cellsin the selected block are turned on by the potential Vread).

If the selected memory cell data is “01”, this selected memory cell isnot turned on by the potential Vcgr01. Due to this, the charges of thebit line BLe are not discharged and the bit line BLe maintains theprecharge potential (about 0.8V).

At period SCLK6, the levels of both SEN ad LAT become “L”, those of bothSENB and LATB become “H”, and the latch circuit LATCH1, i.e., theclocked inverters CINV1 and CINV2, turns into a non-operation state(FIG. 9).

At period SCLK7, if the potential of BLC becomes Vsg (about 4.5V) andthe level of nPRST becomes “L”, the potential of the sense node DTNijbecomes Vdd. At period SCLK8, if the level of nPRST becomes “H”, thesense node turns into a floating state. Further, at period RSCLK9, thepotential of BLCMP becomes Vsense (e.g., about 1.6V) and the potentialof the bit line BLe is transmitted to the sense node.

At this time, if the memory cell data is “11”, “10” or “00”, thepotential of the bit line BLe is not higher than 0.3V. Due to this, thepotential of the sense node DTNij decreases from Vd to a potential ofnot higher than 0.3V. If the memory cell data is “01”, the potential ofthe bit line BLe maintains the precharge potential (about 0.8V).Accordingly, the clamping MOS transistor TN9 (see FIG. 9) is cut off andthe sense node DTNij maintains the potential Vdd.

Thereafter, at period SCLK13, the level of SEN becomes “H”, that of SENBbecomes “L” and the clocked inverter CINV1 turns into an operation state(FIG. 9).

As a result, if the memory cell data is “11”, “10” or “00”, thepotential of the output node Nbij of the clocked inverter CINV1 becomesVdd. If the memory cell data is “01”, the potential of the output nodeNbij of the clocked inverter CINV1 becomes Vss.

At period SCLK14, the level of LAT becomes “H”, that of LATB becomes “L”and the clocked inverter CINV2 turns into an operation state (FIG. 9).Namely, read data (sense node data) is latched by the latch circuitLATCH1.

At this time, if the memory cell data is “11”, “10” or “00”, thepotential of the output node Naij becomes Vss and that of the outputnode Nbij becomes Vdd. If the memory cell data is “01”, the potential ofthe output node Naij becomes Vdd and that of the output node Nbijbecomes Vss.

At period SCLK15, when the potential of DTG1 become Vsg (about 4.5V),the data latched by the latch circuit LATCH1 is transferred to the DRAMcell which is the first feature of the present invention, i.e., the nodeCAP1 ij. Since the capacitor DLN (C1) for latching data is connected tothe node CAP1 ij, read data is latched by the node CAP1 ij.

As a result of the above-stated “READ01” operation, the data latched bythe DRAM cell, i.e., the node CAPA1 ij becomes the data as shown inTable 1.

TABLE 1 CAP1ij after “READ 01” “11” “10” “00” “01” CAP1ij Vss Vss VssVdd

Namely, at this stage, when the potential of the node CAPA1 ij is Vdd(“H”), the even page data is obviously “1”. When the potential of thenode CAPA1 ij is VSS (“L”), it is not clear whether the even page datais “1” or “0”.

Therefore, following the “READ01” operation, “READ10” operation iscarried out.

1.-1.-2. “READ10”

FIG. 24 shows the “READ10” operation.

In the “READ10” operation, the read potential (the potential of theselected word line) is set at Vcgr10 (e.g., 0V) and it is recognizedwhether memory cell data is “11” or other data “10”, “00” or “01”.

The “READ10” operation is almost the same as the “READ01” operationexcept for the level of the read potential (the potential of theselected word line).

First, from periods RCLK1 to RCLK6, the same operation as the “READ01”operation is carried out except for the level of the potential of theselected word line. That is, the potential of the selected word line isset at Vcgr10, the potentials of unselected word lines in the selectedblock are set at Vread and the bit line BLe is precharged and thenturned into a floating state, and the potential of the bit line BLo isset at the ground potential Vss.

Thereafter, at period RCLK7, when the potential SGS of the select gateline SG2 is set at Vread, the potential of the bit line BLe decreases oris maintained according to the selected memory cell data.

Namely, if the selected memory cell data is “11”, the selected memorycell is turned on by the potential Vcgr10. Due to this, the charges ofthe bit line BLe are discharged and the potential of the bit line BLedecreases to 0.3V or lower (while the unselected memory cells in theselected block are turned on by the potential Vread).

On the other hand, if the selected memory cell data is “10”, “00” nor“01”, this selected memory cell is not turned on by the potentialVcgr10. Due to this, the charges of the bit line BLe are not dischargedand the bit line BLe maintains the precharge potential (about 0.8V).

Here, the difference between the “READ10” operation and the “READ01”operation is that at period RCLK7, the potential of REG1 becomes Vdd.

If the potential of REG1 becomes Vdd, the MOS transistor TN10 (FIG. 9)is turned on. Further, since the potential of CAPCRG is Vdd and those ofVREG and DTG2 are Vss, the potential of the node CAP2 ij is Vss. Namely,it is determined whether the sense node DTNij is to be short-circuitedto VREG (Vss) or disconnected from VREG according to the data read inthe “READ01” operation (to be specific, the data latched by the nodeCAP1 ij).

For example, if the data latched by the node CAP1 ij is Vdd (the memorycell data is “01”, see Table 1 above), the MOS transistor TN3 (FIG. 9)is turned on and the sense node DTNij is, therefore, short-circuited toVREG (Vss). As a result, the charges of the bit line BLe are dischargedto VREG and the potential of the bit line BLe changes from the prechargepotential (about 0.8V) to Vss.

If the data latched by the node CAP1 ij is Vss (the memory cell data is“11”, “10” or “00”, see Table 1 above), the MOS transistor TN3 (FIG. 9)is turned off and the sense node DTNij is not, therefore,short-circuited to VREG (VSS). As a result, the potential of the bitline BLe becomes a value according to the selected memory cell data.Namely, if the selected memory cell data is “11”, the potential of thebit line BLe becomes not higher than 0.3V and if “10” or “00”, thepotential of the bit line BLe becomes the precharge potential (about0.8V).

In other words, after the “READ01” operation, at period RCLK8 in the“READ10” operation, if the selected memory cell data is “11” or “01”,the potential of the bit line BLe becomes “L (Vss or a potential nothigher than 0.3V)”. If the selected memory cell data is “10”, or “00”,the potential of the bit line BLe becomes “H (precharge potential)”.

Thereafter, as in the case of the “READ01” operation, the potential ofthe bit line BLe is sensed and latched by the latch circuit LATCH1.

That is to say, at period SCLK6, the levels of both SEN and LAT are setat “L”, those of SENB and LATB are set at “H” and the latch circuitLATCH1, i.e., the clocked inverters CINV1 and CINV2, is turned into anon-operation state.

At period SCLK7, when the potential of BLC is set at Vsg (about 4.5V)and the level of the nPRST is set at “L”, the potential of the sensenode DTNij becomes Vdd. Also, at period SCLK8, when the level of nPRSTbecomes “H”, the sense node becomes a floating state. Further, at periodSCLK9, the potential of BLCLMP becomes Vsense (e.g., about 1.6V) and thepotential of the bit line BLe is transmitted to the sense node.

At this time, if the memory cell data is “11” or “01”, the potential ofthe bit line BLe is either Vs or a potential not higher than 0.3V. Dueto this, the potential of the sense node DTNij decreases from Vdd toeither Vss or a potential not higher than 0.3V. If the memory cell datais “10” or “00”, the bit line BLe maintains the precharge potential(about 0.8V). Thus, the clamping MOS transistor TN9 (see FIG. 9) is cutoff and the sense node DTNij maintains the potential Vdd.

Thereafter, at period SCLK13, the level of SEN becomes “H”, that of SENBbecomes “L” and the clocked inverter CINV1 turns into an operation state(FIG. 9).

As a result, if the memory cell data is “11” or “01”, the potential ofthe output node Nbij of the clocked inverter CINV1 becomes Vdd. If thememory cell data is “10” or “00”, the potential of the output node Nbijof the clocked inverter CINV1 becomes Vss.

Further, at period SCLK14, the level of LAT becomes “H”, that of LATBbecomes “L” and the clocked inverter CINV2 turns into an operation state(FIG. 9). Namely, the read data (sense node data) is latched by thelatch circuit LATCH1.

As a result of the above-stated “READ10” operation, the data latched bythe latch circuit LATCH1 becomes the data as shown in Table 2.

TABLE 2 Read data of even page “11” “10” “00” “01” Naij Vss Vdd Vdd Vss

That is, in case of the memory cell having even page data “1”, thepotential of the output node Naij of the latch circuit LATCH1 becomesVss. In case of the memory cell having even page data “0”, the potentialof the output node Naij of the latch circuit LATCH1 becomes Vdd.

Thereafter, the level of CSLi is set at “H”, thereby outputting the data(even page data) in the latch circuit LATCH1 to the I/O lines (IOj andIO) and externally of the memory chip.

It is noted that FIG. 25 shows the outline of the feature of the readoperation of even page data stated above. Namely, in this embodiment,the read data is latched by the storage circuit (DRAM cell) in the“READ01” operation. Only when the data level is “H” (the memory cell isin the “01” state), the level of the sense node DTNij is forcedly set at“L” in the next “READ10” operation.

Further, in the “READ10” operation, the level of the sense node becomes“L” only when the memory cell is in the “11” state. As a consequence, ifthe memory cell is in the “11” or “01” state (even page data is “1”),the level of the sense node DTNij becomes “L” and if the memory cell isin the “10” or “00” state (even page data is “0”), the level of thesense node DTNij becomes “H”.

1.-2. Read Operation of Odd Page Data

As is obvious from FIG. 20, the “11” state and the “10” state indicateodd page data “1”, and the “00” state and the “01” state indicate theodd page data “0”. That is to say, one read operation “READ00” can judgewhether the odd page data is “1” or “0”. Accordingly, the read operationof the odd page data includes only “READ00”.

1.-2.-1. “READ00”

FIG. 26 shows the “READ00” operation.

In the “READ00” operation, a read potential (the potential of a selectedword line) is set at Vcgr00 (e.g., about 0.7V) and it is recognizedwhether memory cell data is “11”, “10” or “00” or “01”.

The “READ00” operation is almost the same as the “READ01” operationexcept for the level of the read potential (the potential of theselected word line).

First, the potential of the selected word line is set at Vcgr00, thepotentials of unselected word lines in a selected block are set atVread, the bit line BLe is precharged and then turned into a floatingstate, and the potential of the bit line BLe is set at the groundpotential Vss (where BLe is a selected bit line and BLo is a shield bitline).

Thereafter, at period RCLK7, when the potential SGS of the select gateline SG2 is set at Vread, the potential of the bit line BLe decreases oris maintained according to the selected memory cell data.

That is to say, if the selected memory cell data is “11” or “10”, thisselected memory cell is turned on by the potential Vcgr00. Due to this,the charges of the bit line BLe are discharged and the potential of thebit line BLe decreases to 0.3V or lower (while unselected memory cellsin the selected memory cell block are turned on by the potential Vread).

On the other hand, if the selected memory cell data is “00” or “01”,this selected memory cell is not turned on by the potential Vcgr00. Dueto this, the charges of the bit line BLe are not discharged and the bitline BLe maintains the precharge potential (about 0.8V).

Thereafter, as in the same manner as the “READ01” operation, thepotential of the bit line BLe is sensed and latched by the latch circuitLATCH1.

That is, at period SCLK6, the levels of both SEN and LAT are set at “L”,those of SENB and LATB are set at “H” and the latch circuit LATCH1,i.e., the clocked inverters CINV1 and CINV2, is turned into anon-operation state.

At period SCLK7, when the potential of BLC is set at Vsg (about 4.5V)and the level of nPRST is set at “L”, then the potential of the sensenode DTNij becomes Vdd. At period SCLK8, when the level of the nPRSTbecomes “H”, the sense node is turned into a floating state. At periodSCLK9, the potential of BLCLMP becomes Vsense (e.g., about 1.6V) and thepotential of the bit line BLe is transmitted to the sense node.

At this time, if the memory cell data is “11” or “10”, the potential ofthe bit line BLe is not higher than 0.3V. Due to this, the potential ofthe sense node DTNij decreases from Vdd to a potential of not higherthan 0.3V. Further, if the memory cell data is “00” or “01”, the bitline BLe maintains the precharge potential (about 0.8V). Thus, theclamping MOS transistor TN9 (see FIG. 9) is cut off and the sense nodeDTNij maintains the potential Vdd.

Thereafter, at period SCLK13, the level of SEN becomes “H”, that of SENBbecomes “L”, and the clocked inverter CINV1 turns into an operationstate (FIG. 9).

As a result, if the memory cell data is “11” or “10”, the potential ofthe output node Nbij of the clocked inverter CINV1 becomes Vdd. If thememory cell data is “00”, or “01”, the potential of the output node Nbijof the clocked inverter CINV1 becomes Vss.

Further, at period SCLK14, the level of LAT becomes “H” and that of LATBbecomes “L”, and the clocked inverter CINV2 turns into an operationstate (FIG. 9). That is, the read data (sense node data) is latched bythe latch circuit LATCH1.

As a result of the “READ00” operation stated above, the data latched bythe latch circuit LATCH1 becomes the data as shown in Table 3.

TABLE 3 Read data of odd page “11” “10” “00” “01” Naij Vss Vss Vdd Vdd

That is to say, in case of the memory cell having odd page data “1”, thepotential of the output node Naij of the latch circuit LATCH1 is Vss. Incase of the memory cell having odd page data “0”, the potential of theoutput node Naij of the latch circuit LATCH1 is Vdd.

Thereafter, the level of CSLi is set at “H”, thereby outputting the data(odd page data) of the latch circuit LATCH1 to the I/O lines (IOj, nIOj)and externally of the memory chip.

It is noted that FIG. 27 shows the outline of the feature of the readoperation of odd page data. Namely, in this embodiment, the data read inthe “READ00” operation becomes odd page data as it is. Accordingly, inthe odd page data read operation, only the latch circuit (SRAM cell)LATCH1, for example, is used and the DRAM cell is not used.

2. Program Operation

As outlined by FIGS. 21 and 22, the program operation consists of twoprogram operations, i.e., an even page data program operation and an oddpage data program-operation.

2.-1. Program Operation of Even Page Data

First, the outline (operation flow) of the program operation of evenpage data will be described and then the concrete circuit operationthereof (operation timing) will be described.

FIG. 28 shows the outline of the program operation of even page data.

First, an “80 (hexadecimal)” command is inputted into the chip. Later,an address signal is inputted into the chip and even page program datais inputted into the chip. This program data is inputted into the latchcircuit LATCH1 (FIG. 9) in the data circuit through the I/O lines IOjand nIOj in the chip (in steps ST1 to ST2).

Next, a “10 (hexadecimal)” command is inputted into the chip. Then, aprogram pulse is supplied to the word line of a memory cell (in stepsST3 to ST4).

Here, for the purpose of shortening program time (accelerating theprogram), this embodiment adopts a sequence (parallel processing) fordetecting whether “10”-programming has been carried out sufficiently bysupplying a program pulse the (n−1)-th time (a step ST5) as well assupplying a program pulse the n-th time (the step ST4).

As shown below, as another means for realizing shortened program time(acceleration of the program), this embodiment adopts a sequence forgradually increasing a program potential (magnitude of the programpulse) and not to conduct “10” verify-read at the beginning of theprogram operation.

In this embodiment, therefore, if the “10” verify-read is not conducted,a detection as to whether or not programming has been sufficientlyconducted (the step ST5), is not made, either.

If the number of times at which a program pulse is supplied to the wordline is not more than a predetermined number of times (e.g., ninetimes), the “10” verify-read is omitted and program pulses arecontinuously supplied (in a step ST6). This is because the program canbe accelerated by omitting the verify-read at the beginning of theprogram operation.

The “10” verify-read (VERIFY10) means that in the verification forverifying whether data “10” has been successfully programmed into amemory cell to which “10”-programming is conducted, the memory cell datais read at a verify-read potential Vcgv10 (FIG. 20) so as to make theverification.

In this embodiment, the program potential (program pulse level) is setat an initial value and the supply of a program pulse starts.Thereafter, every time a program pulse is applied, the program potentialapplied to the word line is gradually increased by a predetermined value(e.g., about 0.2V).

For example, by increasing the program potential by about 0.2V, thewidth of the threshold voltage distribution of the memory cell in the“10”-programming state can be ideally set at about 0.2V. In the actualoperation, the width of the threshold voltage distribution of the memorycell in the “10”-programming state is about 0.4V due to so-called arraynoise generated during the verify-read operation.

In FIG. 20, it is assumed that the width of the threshold voltagedistribution of the memory cell in the program state (“10”, “00” or“01”) is about 0.4V.

During a period from the start of the program operation until the supplyof program pulses, for example, nine times, the program potential is setsufficiently low and the memory cell to the “10”-programming isconducted is not excessively programmed (programmed so that thethreshold voltage exceeds Vcgr00).

The reason that pulses having a low program potential is applied to theword line at the beginning, and every time a pulse is supplied, theprogram potential is gradually increased, is to gradually injectelectrons into the floating gate electrode and finally accumulate apredetermined amount of electrodes in the floating gate electrode.

In that case, compared with a case of, for example, injecting apredetermined amount of electrons into the floating gate electrode byone program pulse, an electric filed applied to the tunnel oxide film ofthe memory cell by one program pulse is low and the reliability of thetunnel oxide film is, therefore, improved.

Further, the program potential (program pulse level) is graduallyincreased from a lower value to a higher value. Namely, in case ofgradually increasing the program potential, the width of the thresholdvoltage distribution of the memory cell can be empirically narrowedcompared with a case of setting an initial program potential at a highvalue and gradually decreasing this program potential.

If the number of times at which program pulses are supplied to the wordline is, for example, 10 times or more, after program pulses aresupplied to the word line, “10” verify-read is carried out (in steps ST6to ST7) so as to verify whether or not the data “10” has beensuccessfully programmed into the memory cell to which the“10”-programming is conducted.

Further, the data read from the memory cell by the “10” verify-read isdata indicating whether “10”-programming has been sufficiently carriedout, and the data is stored in the latch circuit LATCH1 in the datacircuit.

Then, when the next program pulse is supplied to the word line (in thestep ST4), an operation for verifying whether “10”-programming has beensufficiently carried out by the previous program pulse (ProgramCompletion Detection) is executed based on the data in the latch circuitLATCH1 (in a step ST5).

To be specific, as shown in FIG. 21, in the even page data programoperation, “11”-programming and “10”-programming are included.“11”-programming means maintaining the erase state (“11”).“10”-programming means increasing the threshold voltage by programpulses and changing the “11” state into the “10”, state.

If predetermined data “11” or “10” has been sufficiently programmed intoall selected memory cells (columns) (or, actually, if data “10” has beensuccessfully programmed into the memory cell to which the“10”-programming is conducted), the even page data program operation iscompleted.

If the predetermined data “11” or “10” has not been sufficientlyprogrammed into at least one selected memory cell (column) (or,actually, the data “10” has not been sufficiently programmed into allmemory cells to which “10”-programming is conducted), the “10”verify-read operation and the supply of program pulses are continued.

Normally, thereafter, a high electric field is not applied to the tunneloxide film of the memory cell which has been programmed sufficiently anda high electric field is applied to the tunnel oxide films of only thememory cells which have not been programmed sufficiently, therebypreventing excessively programming the memory cells having good programcharacteristics.

In the meantime, in this embodiment, the operation for detecting whetherthe program is carried out sufficiently/insufficiently (ProgramCompletion Detection) is executed simultaneously with the operation forthe supply of a program pulse to the word line. Alternatively, theprogram completion detection may be carried out right after the “10”verify-read and, if the result of the program completion detection isnot satisfactory, a program pulse may be applied again.

The outline of the program operation of the even page data has beendescribed so far.

As stated above, the even page data program operation consists of thesupply of program pulses, the “10” verify-read (VERIFY10) and theprogram completion detection (detection as to whether or not program hasbeen carried out sufficiently).

Now, these three operations will be described one by one in detail.

2.-1.-1 Supply of Program Pulse

FIG. 29 shows operation timing relating to the supply of program pulses.

At the data circuit (column) side, if “10”-programming is conducted(even page data “0” is programmed into a memory cell), program data isinputted into the latch circuit LATCH1 (FIG. 9) externally of the memorychip and the node Naij of the latch circuit LATCH1 is latched to “L”.

If “11”-programming is conducted (even page data “1” is programmed intoa memory cell), program data is inputted into the latch circuit LATCH1(FIG. 9) externally of the memory chip and the node Naij of the latchcircuit LATCH1 is latched to “H”.

At the word line control circuit (row) side, first, the level of RDECPBis set at “L” in the row decoder (FIGS. 16 and 18). At this time, thelevels of both RDECAD (FIG. 16) and RDECADS1 (FIG. 18) are “L (Vss)” andall memory cell blocks are in an unselected state.

Thereafter, the level of RDECPB is changed from “L” to “H”. At thismoment, the MOS transistor TP4 is turned off and the MOS transistor TN21is turned on (FIGS. 16 and 18).

Further, in a selected memory cell block, the levels of all row addresssignals AROWi, . . . AROWj become “H” and the levels of both RDECAD(FIG. 16) and RDECADS1 (FIG. 19) become “H”. In unselected memory cellblocks, since the level of at least one of the row address signalsAROWi, . . . AROWj is “L”, RDECAD (FIG. 16) and RDECADS1 (FIG. 18)maintain “L”.

In the word line driver (FIGS. 17 and 19) in the selected memory cellblock, since the levels of the input signals RDECAD and RDECADS1 become“H”, the high voltage switching circuit (NMOS charge-pumping circuit) 26is actuated by an oscillation signal (clock signal) Owc.

Accordingly, in the word line driver (FIGS. 17 and 19) in the selectedmemory cell block, a boosting potential VpgmH (a potential higher thanthe program potential Vpgm by about 2V) generated based on the potentialVRDEC is transferred to the output node of the high voltage switchingcircuit 26.

For example, if the word line driver RMAIN1 (FIG. 17) in the firstmemory cell block is selected, the potential VpgmH (e.g., about 18 to22V) is transferred to the output node TransferG1. If the word linedriver RMAIN2 (FIG. 19) in the second memory cell block is selected, thepotential VpgmH is transferred to the output node TransferG2.

As a result, the gates of the transfer transistors HNt1, HNt2, . . .HNt16 have sufficiently high potentials and the potentials of the signallines CG1, CG2, . . . CG16 are transferred to the word lines (controlgate lines) WL1, WL2, . . . WL16 through the transfer transistors HNt1,HNt2, . . . HNt16, respectively, without so-called threshold drop.

Also, the potentials of the signal lines SGD and SGS are transferred tothe select gate lines SG1 and SG2 through the transfer transistors HN5and HN6, respectively.

Here, among the signal lines CG1, CG2, . . . CG16, the potential of oneselected signal line is set at Vpgm (e.g., about 16 to 20V) by theswitching circuit (FIG. 8) and the potentials of the remainingunselected signal lines are set at Vpass (e.g., about 10V) by theswitching circuit (FIG. 8).

Further, the potential of the signal line SGD is set at Vdd and that ofthe signal line SGS is set at Vss.

In the word line drivers (FIGS. 17 and 19) in unselected memory cellblocks, the potentials of RDECAD and RDECADS2 are transferred to theoutput nodes TransferG1 and TransferG2 of the high voltage switchingcircuit 26, respectively.

Namely, in the word line drivers (FIGS. 17 and 19) in the unselectedmemory cell blocks, the potentials of both the output nodes TransferG1and TransferG2 become the ground potential Vss.

As a result, the transfer transistors HNt1, HNt2, . . . HNt16 are turnedoff and the word lines (control gate lines) WL1, WL2, . . . WL16 areturned into a floating state. The select gate lines SG1 and SG2 aregrounded by the signal lines SGS and SGD, respectively.

The operation timing shown in FIG. 29 will be described in detail.

It is noted that description will be given while assuming that a memorycell connected to the bit line BLe is selected.

At the row side (word line control circuit side), at period PLCK1, thelevel of BSTON becomes “H”. At this time, in the selected memory cellblock, the potential Vdd (RDECAD or RDECADS2) is transferred to theoutput node (TransferG1 or TransferG2) of the high voltage switchingcircuit in the word line driver.

At period PCLK3, the level of BSTON becomes “L”. At period PCLK4, thepotential of VRDEC becomes VpgmH. Due to this, in the selected memorycell block, the potential of the output node (TransferG1 or TransferG2)of the high voltage switching circuit in the word line driver rises toVpgmH.

At the column side (data circuit side), on the other hand, at periodPCLK1, the potentials of BLC and BLCLMP become Vsg (e.g., about 6V) andat period PCLK4, the potential of BLSe becomes VsgHH. As a result, thelatch circuit LATCH1 and the bit line BLe are electrically connected toeach other and the data in the latch circuit LATCH1 is transferred tothe bit line BLe.

For example, the potential Vss is transferred from the latch circuitLATCH1 to a bit line (selected bit line) BLe to which a memory cell, towhich the “10”-programming is conducted, is connected (while thepotential of the node Naij of the latch circuit is Vss). Also, thepotential Vdd is transferred from the latch circuit LATCH1 to the bitline (selected bit line) BLe to which a memory cell, to which“11”-programming is conducted, (a memory cell maintained in an erasestate) is connected (while the potential of the node Naji of the latchcircuit is Vdd).

The potential of the unselected bit line BLo is set at Vdd. Namely, thepotential of BLSo is always set at Vss. At period PLCK4, the potentialof BIASo becomes VsgHH and that of BLCRL becomes Vdd, so that thepotential Vdd is transferred from BLCRL to the bit lines BLo.

Then, after completing charging the bit lines BLe and BLo, at periodPCLK5, the potentials of unselected word lines CG unselect are set atVpass (e.g., about 10V). At period PCLK6, the potential of the selectedword line CG select is set at Vpgm (e.g., about 16 to 20V).

The potential of the selected bit line BLe to which a memory cell, towhich “10”-programming is conducted, is connected is Vss. Due to this,the channel potential of the memory cell is Vss, as well. Accordingly,in the memory cell to which “10”-programming is conducted, a highelectric field is applied between the channel and the control gateelectrode (selected word line) and electrons are injected from thechannel into the floating gate electrode.

The potential of the bit line BLe to which a memory cell, to which“11”-programming is conducted, is Vdd and that of the select gate lineSG1 is Vdd, as well. That is, the select transistor connected betweenthe memory cell, to the “11”-programming is conducted, and the bit lineis cut off.

Consequently, if the potentials of the unselected word lines becomeVpass and the potential of the selected word line becomes Vpgm, thechannel potential of the memory cell, to the “11”-programming isconducted, rises up to about 8V by the capacitive coupling between thechannel of the memory cell, to which “11”-programming is conducted, andthe word line.

As a result, in the memory cell to which “11”-programming is conducted;a high electric field is not applied between the channel and the controlgate electrode (selected word line) and no electrons are injected fromthe channel into the floating gate electrode (which means that“10”-programming is inhibited, that is, the erase state is maintained).

Meanwhile, the potential of the bit line BLo is Vdd. Therefore, if thepotential of the select gate SG1 becomes Vdd, the select transistorconnected to the bit line BLo is cut off. That is, in unselected memorycells connected to the bit lines BLo, channel potential rises and“10”-programming is inhibited.

It is noted that the program pulse is supplied to the selected word lineduring time from period PCLK6 until period CCLK10/PRCV1.

At period PRCV1, the charges of the selected word line are discharged tochange the potential of the selected word line from Vpgm to Vss. Atperiod PRCV2, the charges of the unselected word lines are discharged tochange the potentials of the unselected word lines from the transferpotential Vpass to Vss. Further, at period PRCV3, the charges of the bitlines BLE and BLo are discharged.

FIG. 30 shows a state in which a program pulse is supplied. Namely, ifeven page data is “00”, the ground potential Vss (“L”) is transferred tothe channel of the program cell. If even page data is “1”, the potentialof the program cell is Vdd−Vth and in a floating state.

2.-1.-2. “VERIFY10”

FIG. 31 shows operation timing for “10” verify read.

In the “10” verify-read (VERIFY10) operation, after the bit line isprecharged, the potential of a selected word line is set at Vcgv10(e.g., about 0.15V), a change in the potential of the bit line isdetected and memory cell data is read.

Here, since program data is already latched by the latch-circuit LATCH1(FIG. 9), it is necessary not to collide the read data against theprogram data in the verify-read operation.

To prevent such collision, while precharging and discharging the bitline (reading cell data), the program data stored in the latch circuitLATCH1 is transferred to the node CAP2 ij and temporarily storedtherein.

More concrete description will be given hereinafter.

First, at period PCLK1, the potentials of CAPCRG and VREG are set atVdd. At period RCLK, the potential of BOOT is set at Vss. At periodRCLK5, when the potential of VREG becomes Vss, the potential of the nodeCAP3 ij is reset at Vss. During these periods, the potential of DTG2 isVss.

At period RCLK9/SCLK1, the potential of CAPCRG becomes Vss and the nodeCAP2 ij turns into a floating state. Then, at period SCLK2, thepotential of DTG2 becomes Vsg (e.g., about 4.5V) and the program datalatched by the latch circuit LATCH1 is transferred to the node CAP2 ijby way of the MOS transistor TN2 and is temporarily stored therein.

In other words, if even page program data is “0” (“10”-programming isconducted), the level of the node Naij of the latch circuit LATCH1 is“L” and the potential of the node CAP2 ij, therefore, becomes Vss.

If even page program data is “1” (“11”-programming is conducted, thelevel of the node Naij of the latch circuit LATCH1 is “H” and thepotential of the node CAP2 ij, therefore, becomes Vdd.

Then, at period SCLK3, the potential of DTG2 becomes Vdd and at periodSCLK4, the potential of BOOT becomes Vdd.

Here, if even page program data is “0” (“10”-programming is conducted),the potential of the node CAP2 ij remains Vss. If even page program datais “1” (“11”-programming is conducted), the potential of the node CAP2ij is booted by the capacitor DLN (C2) and rises from Vdd (e.g., about2.3V) to about 3.5V.

Thereafter, at period SCLK5, the potential of DTG2 becomes Vss and thenode CAP2 ij is electrically disconnected from the latch circuit LATCH1.

On the other hand, the memory cell data is read to the bit line BLe inthe same manner as the ordinary read operation (READ10).

Namely, after precharging the bit line BLe or the like, at period RCLK7,the potential of the SGS becomes Vread and that of the bit line BLechanges according to the memory cell data.

For example, in the selected memory cell to which “11”-programming isconducted (the selected memory cell having even page program data “1”),the selected memory cell is turned on by the potential Vcgv10. Due tothis, the charges of the bit line BLe are discharged and the potentialof the bit line BLe becomes not higher than 0.3V.

Further, in the selected memory cell to which “10”-programming isconducted (in the selected memory cell having even page program data“0”), if “10”-programming is insufficient, the selected memory cell isturned on by the potential Vcgv10. Due to this, the charges of the bitline BLe are discharged and the potential of the bit line BLe becomesnot lower higher than 0.3V.

In the selected memory cell to which “10”-programming is conducted (theselected memory cell having even page program data “0”), if“10”-programming is sufficient, the selected memory cell is turned offby the potential Vcgv10. Due to this, the charges of the bit line BLeare not discharged and the potential of the bit line BLe is maintained0.8V.

Thereafter, at period SCLK6, the levels of both SEN and LAT become “L”,those of both SENB and LATB become “H” and the latch circuit LATCH1 inthe data circuit, i.e., clocked inverters CINV1 and CINV2, turns into anon-operation state.

At this moment, the program data has been already transferred to thenode CAP2 ij and at period SCLK5, the node CAP2 ij has been alreadyelectrically disconnected from the latch circuit LATCH1.

At period SCLK7, since the potential of BLC becomes Vsg (e.g., about4.5V) and the level of nPRST becomes “L”, the sense node DTNij ischarged and the potential of the sense node becomes Vdd (while thepotential of Naij becomes Vdd, as well). At period SCLK8, when thepotential of nPRST becomes Vdd, the sense node DTNij turns into afloating state.

At period SCLK9, when the potential of BLCLMP becomes Vsense (e.g.,about 1.6V), the memory cell data read to the bit line BLe istransferred to the sense node DTNij.

Namely, as for a memory cell which has been programmed insufficientlyout of the selected memory cell to which “11”-programming is conducted(the selected memory cell having even page program data “1”) and theselected memory cell to which “10”-programming is conducted (theselected memory cell having even page program data “0”), the potentialof the bit line BLe is not higher than 0.3V and that of the sense nodeDTNij decreases to a potential not higher than 0.3V, as well.

As for a memory cell which has been programmed sufficiently out of theselected memory cells to which “10”-programming is conducted (theselected memory cell having even page program data “0”), the potentialof the bit line BLe is maintained 0.8V. Due to this, the clamping MOStransistor TN9 is cut off and the sense node DTNij maintains thepotential Vdd.

At period SCLK10, the potential of the sense node DTNij becomes thepotential as shown in Table 4.

TABLE 4 Sense node (DTNij·Naij) in “VERIFY 10” “10”- “11”-programming“10”-programming programming (Write inhibit) Deficient Sufficient Pointof “LOW” “LOW” “HIGH” SCLK 10 Point of “HIGH” “LOW” “HIGH” SCLK 12

Thereafter, differently from the ordinary read operation (READ10), atperiod SCLK11, the potential of REG2 becomes Vsg and the MOS transistorTN6 is turned on in the “10” verify read operation.

If “11”-programming is conducted (even page program data is “1”), thenode CAP2 ij is latched to “H” and the MOS transistor TN1 is, therefore,turned on. That is, the COMi (set at Vdd) and the sense node DTNij areshort-circuited, with the result that the potential of the sense nodeDTNij becomes Vdd.

If “10”-programming is conducted (even page program data is “0”), thenode CAP2 ij is latched to “L” and the MOS transistor TN1 is, therefore,turned off. That is, the COMi (set at Vdd) and the sense node DTNij areelectrically disconnected from each other and the potential of the sensenode DTNij has no change.

Accordingly, at period SCLK12, the potential of the sense node DTNijbecomes the potential as shown in the above table 4.

Then, at period SCLK13, the potential of SEN becomes Vdd, that of SENBbecomes Vss, and the clocked inverter CINV1 turns into an operationstate to thereby sense the potential of the sense node DTNij.

As shown in Table 4 above, if “11”-programming is conducted and“10”-programming is sufficient, the level of the sense node DTNij is“H”. Due to this, the potential of the output node Nbij of the clockedinverter CINV1 becomes Vss. If “10”-programming is deficient, the levelof the sense node DTNij is “L” and the potential of the output node Nbijof the clocked inverter CINV1, therefore, becomes Vdd.

Thereafter, at period SCLK14, the potential of LAT becomes Vdd, that ofLATB becomes Vss and read data is latched by the latch circuit LATCH1.

That is to say, if “11”-programming is conducted and “10”-programming isdeficient, the potential of the node Naij becomes Vdd and that of thenode Nbij becomes Vss. If “10”-programming is deficient, the potentialof the node Naij becomes Vss and that of the node Nbij becomes Vdd.

The data in the latch circuit LATCH1 at a point at which the “10” verifyread operation is completed becomes the data as shown in Table 5.

TABLE 5 Data of latch circuit LATCH1 after “VERIFY 10” “11”-programming“10”-programming “10”-programming (Write inhibit) Deficient SufficientNaij “Vdd” “Vss” “Vdd” Nbij “Vss” “Vdd” “Vss”

The data in the latch circuit LATCH1 is later used as new program data(even page data). Namely, in the “VERIFY10” operation, the data latchedby the node CAP2 ij is erased in Program completion detection which willbe described later.

By doing so, if program data (even page data) is “0” (i.e., “L”), theprogram (“10”-programming) is executed. If program is deficient, theprogram data is changed from “0” (“L”) to “1” (“H”) and the program(“10”-programming) is not executed thereafter.

In the meantime, in the above-stated “10” verify-read operation, atperiod SCLK4, the potential of BOOT is changed from Vss to Vdd and thatof the node CAP2 ij in case of “11”-programming is booted to about 4V.This is because the sense node DTNij is to be set at Vdd without thethreshold drop corresponding to the threshold voltage of the N channelMOS transistor TN1 when the potential of REG2 is set at Vsg at periodSCLK11.

Providing that the potential of the node CAP2 ij is Vdd (e.g., about2.3V) in case of “11”-programming, the sense node DTNij rises only toabout 1.5V at period SCLK11.

While it is considered that the potential of the sense node, i.e., 1.5Vcan be recognized as “H” in logical operation, a through currentdisadvantageously flows into the clocked inverter CINV1 during the senseoperation (at period SCLK13). Since the number of data circuits in achip is 4,000, 8,000 or 16,000, if a through current flows into theclocked inverters CINV1 of all of the data circuits, the total currentbecomes as high as about 100 mA.

As a result, the internal power supply potential Vdd disadvantageouslydrops or consumption current increases considerably.

As described in this embodiment, if the potential of the node CAP2 ij incase of “11”-programming is booted to about 4V, the sense node DTNij canbe charged without the threshold drop at the MOS transistor TN1 and itis possible to prevent the power supply potential Vdd from dropping orconsumption current from increasing as stated above.

FIG. 32 shows the outline of the “10” verify-read operation. Namely,after the program data latched by the latch circuit LATCH1 istransferred to the DRAM cell, the read data is transferred to the sensenode DTNij.

At this time, if the data latched by the DRAM cell is “H”, i.e., thedata indicates that “11”-programming is conducted “10”-programming issufficient, the level of the sense node DTNij becomes “H” irrespectivelyof the read data.

That is to say, only when the data latched by the DRAM cell is “L”,i.e., the data indicates that “10”-programming is deficient, the dataaccording to the memory cell state is transferred to the sense nodeDTNij.

For example, if the memory cell state does not reach the “10” state(“10”-programming is deficient), the level of the sense node DTNijbecomes “L”. If the memory cell state reaches the “10” state(“10”-programming is sufficient), the level of the sense node DTNijbecomes “H”.

The data of the sense node DTNij is latched by the latch circuit LATCH1.

Following the above, the next program pulse is supplied and the next“10” verify-read operation is conducted based on the data latched by thelatch circuit LATCH1.

2.-1.-3. “Program Completion Detection”

After “VERIFY10”, “Program completion detection” operation for detectingwhether or not “10”-programming has been successfully conducted to allmemory cells to “10”-programming is conducted, is carried out. Thisdetection is made based on the data (see Table 5) latched by the latchcircuit LATCH1 in the “VERIFY10” operation. If “10”-programming isdetected to be deficient, reprogram (supply of program pulses) isexecuted. If “10”-programming is sufficient, the program (supply ofprogram pulses) is completed.

FIG. 33 shows the operation timing of “Program completion detection”operation.

In this “Program completion detection” operation, the batch detectioncircuit shown in FIG. 12 is used.

As described in the outline of operation with reference to FIG. 26,after the completion of “VERIFY10”, the next “supply of programmingpulses” is instantly started and “Program completion detection” isexecuted in parallel to the “supply of “programming pulses”.

Accordingly, period PCLK7/CCLK1 is the same as the period PCLK7/CCLK1shown in FIG. 29.

Further, in “Program completion detection” during the program operationof even page data, the period CCLK5 in FIG. 33 becomes the period CCLK9.Namely, operations until the period CCLK5 are executed and those fromperiods CCLK5 to CCLK9 are omitted.

It is noted that the operations from periods CCLK5 until CCLK9 areexecuted in “Program completion detection” in the program operation ofodd page data to be described later.

First, at period CCLK1, the potential of CAPCRG becomes Vsg and that ofVreg becomes Vdd, the node CAP2 ij is charged and the potential of thenode CAP2 ij becomes Vdd (while the potential of DTG2 is Vss).

At this time, the data (even page data) latched by the node CAP2 ij in“VERIFY10” is erased. However, since new-program data has been alreadylatched by the latch circuit LATCH1 in “VERIFY10”, program data is notcompletely erased.

That is, when program data (even page data) is “0” (i.e., “L”), theprogram (“10”-programming) is executed. If the program is sufficient,the program data is changed from “0” to “1” and the program(“10”-programming) is not executed thereafter.

Then, at period CCLK2 (DCLK1), when the potential of COMHn (FIG. 12) ischanged from Vss to Vdd and that of NCOML (FIG. 12) is changed from Vddto Vss, the potentials of COMi1 and COMi2 become Vdd and turn into afloating state and the potential of NCOM becomes Vss and turns into afloating state.

At period DCLK2, the potential of REG2-0 becomes, for example, Vdd. Atthis time, in FIG. 12, the first to fifth data circuits are selected,and the potential of REG2 in the first data circuit and that of REG2 inthe fifth data circuit become Vdd.

In both the first and fifth data circuits, if the potential of the nodeNaij of the latch circuit LATCH1 is Vdd (see Table 5), i.e.,“11”-programming (write inhibit) is conducted or “10”-programming issufficient, then the sense node DTNij maintains the potential Vdd. Thus,the MOS transistor TN6 (FIG. 9) is turned off and COMi1 and COMi2maintain the potential Vdd. Accordingly, NCOM maintains the potentialVss.

On the other hand, if the potential of the data of the node Naij of thelatch circuit LATCH1 is Vss (see Table 5) in at least one of the firstand fifth data circuits, i.e., if “10”-programming is deficient, thenthe sense node DTNij maintains the potential Vss. Due to this, the MOStransistor TN6 (FIG. 9) is turned on and the potentials of COMi1 orCOMi2 changes from Vdd to Vss. Accordingly, the potential of NCOMchanges from Vss to Vdd.

Likewise, the potentials of REG2-1, REG2-2 and REG2-3 sequentiallybecome Vdd. Namely, when the potential of REG2-1 is Vdd, the second andsixth data circuits are selected. When the potential of REG2-2 is Vdd,the third and seventh data circuits are selected. When the potential ofREG2-3 is Vdd, the fourth and eighth data circuits are selected. In eachdata circuit, a state of the latch circuit LATCH1, i.e., whether“10”-programming is sufficient/deficient, is detected.

As a result, if data indicating that “11”-programming (write inhibit) isconducted or that “10”-programming is sufficient is outputted from allof the first to eighth data circuits, the potential of NCOM becomes Vssat period CCLK3. Further, if data indicating that “10”-programming isdeficient is outputted from at least one of the first to eighth datacircuits, the potential of NCOM becomes Vdd at period CCLK3.

Furthermore, all columns are connected in parallel to the FLAG node(FIG. 12). Accordingly, the FLAG node is preset to have the potentialVdd and in a floating state. Then, at period CCLK3, the potential ofCOLPRE is set at Vdd and the MOS transistor TN17 (FIG. 12) is turned on.

At this time, if data indicating that “11”-programming (write inhibit)is conducted or that “10”-programming is sufficient is outputted fromall data circuits corresponding to all columns, the potential of NCOM isVss and the MOS transistor TN16 (FIG. 12) is, therefore, turned off.Accordingly, the FLAG node maintains the potential Vdd.

Further, if data indicating that “10”-programming is deficient isoutputted from at least one of all data circuits corresponding to allcolumns, the potential of NCOM becomes Vdd and the MOS transistor TN16(FIG. 12) is, therefore, turned on. Accordingly, the potential of theFLAG node changes from Vdd to Vss.

As can be understood from the above description, only when a memory cellto which “10”-programming has been conducted deficiently, does not existin all columns, the FLAG node maintains the potential Vdd. If a memorycell to which “10”-programming has been conducted deficiently, exists inat least one column, the potential of the FLAG node changes to Vss.

Therefore, if the level of this FLAG node is detected and the potentialof the FLAG node is Vdd, i.e., there does not exist a column (memorycell) for which “10”-programming is deficient, an even page data programroutine is finished. If the potential of the FLAG node is Vss, i.e.,there exists at least one column (memory cell) for which“10”-programming is deficient, “10” verify-read is conducted again andthen Program completion detection is conducted in parallel with thesupply of a program pulse.

In a fail column replaced by a spare cell by the redundancy circuit dueto the presence of a fail cell (it is assumed that a replacement unit iseight columns), the fuse element of the batch detection circuit 10 shownin FIG. 12 is cut off. Accordingly, the potential of the FLAG node doesnot become Vss because of such a fail column.

FIG. 34 shows the outline of Program completion detection. Namely, thedata read from the memory cell in the “10” verify-read operation islatched by the latch circuit LATCH1. Therefore, if the data in the latchcircuit LATCH1 is transferred to the sense node DTNij and the potentialchange of COMi is detected, then it is possible to detect whether or not“10”-programming is completed for all memory cells.

2.-2. Program Operation of Odd Page Data

First, the outline (operation flow) of the program operation of odd pagedata will be described and then the concrete circuit operation thereof(operation timing) will be described.

FIG. 35 shows the outline of the program operation of odd page data.

Before conducting odd page data programming, the even page data programas described above has been already completed. Therefore, the memorycell state is “11” or “10” state.

First, an “80 (hexadecimal)” command, for example, is inputted into thechip. Then, an address signal is inputted into the chip and odd pageprogram data is inputted into the latch circuit LATCH1 (FIG. 9) in thelatch circuit through the I/O lines IOj and nIOJ (in steps ST1 to ST2).

Next, a “10 (hexadecimal)” command, for example, is inputted into thechip. Then, the even page data stored in the memory cell is read(Internal Data Load). Thereafter, based on the odd page data (programdata) inputted externally of the chip and the even page data read fromthe memory cell, the supply of a program pulse is executed (in steps ST3to ST5).

Here, in this embodiment, for the purpose of shortening program time(accelerating the program), this embodiment adopts a sequence (parallelprocessing) for detecting whether “00”-programming and “01”-programminghave been carried out sufficiently by supplying a program pulse the(n−1)-th time as well as supplying a program pulse the n-th time (insteps ST5 to ST7).

However, as shown below, as another means for realizing shortenedprogram time (accelerated program), this embodiment adopts a sequencefor gradually increasing a program potential (the magnitude of a programpulse) and not to conduct “00” verify-read and “01” verify-read at thebeginning of the program operation.

In this embodiment, therefore, if the “00” verify-read is not conducted,a detection as to whether or not “00”-programming has been sufficientlyconducted, is not made. Further, if “01” verify-read is not conducted, adetection as to whether or not “01”-programming has been sufficientlyconducted, is not made, either.

If the number of times at which a program pulse is supplied to the wordline is not higher than the first predetermined number of times (e.g.,nine times), the “00” verify-read is omitted and program pulses arecontinuously supplied (in a step ST10). If the number of times at whicha program pulse is supplied to the word line is not higher than thesecond predetermined number of times (e.g., 13 times), the “01”verify-read is omitted (in steps ST8A and 8B).

As can be seen, the reason for omitting the verify read operation at thebeginning of the program is that with a method of gradually increasingthe program potential as stated above, there is little possibility thatpredetermined data is programmed into the memory cell at the beginningof the program and it is, therefore, advantageous to omit theverify-read operation and accelerate program speed rather thanconducting the verify-read operation at the beginning of the program.

The “00” verify-read (VERIFY00) means that memory cell data is read witha verify read potential Vcgv00 (FIG. 20) in verification to verifywhether or not data “00” has been programmed into a memory cell to which“00”-programming is conducted.

The “01” verify-read (VERIFY01) means that memory cell data is read witha verify read potential Vcgv01 (FIG. 20) in verification to verifywhether or not data “01” has been programmed into a memory cell to which“01”-programming is conducted.

In this embodiment, the program potential (program pulse level) is setat an initial value and the supply of a program pulse starts. Then,every time a program pulse is supplied, the program potential applied tothe word line is gradually increased by a predetermined value (e.g.,about 0.2V).

For example, by increasing the program potential by about 0.2V, thewidth of the threshold voltage distribution of the memory cell in the“00”-programming state and that of the memory cell in the“01”-programming state can be ideally made about 0.2V. In actualoperation, due to array noise generated during the verify-readoperation, the width of the threshold voltage distribution of the memorycell in the “00”-programming state and that of the memory cell in the“01”-programming state become about 0.4V.

During the period from the start of the program operation until aprogram pulse is supplied to the word line the ninth time, the programpotential is set at a low value sufficient to completely conduct“00”-programming. Further, during the period from the start of theprogram operation until a program pulse is supplied the 13th time, theprogram potential is set at a low value sufficient to completely conduct“01”-programming.

Accordingly, the memory cell to which “00”-programming is conducted andthe memory cell to which “01”-programming is conducted, is notexcessively programmed (programmed so that the threshold voltage exceedsVcgr01).

In this way, at the beginning of the operation, a pulse having a lowprogram potential is supplied to the word line. Every time a pulse issupplied, the program potential is gradually increased. This is becauseelectrons are gradually injected into the floating gate electrode andfinally a predetermined amount of electrons are injected into thefloating gate electrode.

In that case, compared with a case where a predetermined amount ofelectrons are injected into the floating gate electrode with one programpulse, an electric field applied to the tunnel oxide film of the memorycell with one program pulse is low, thereby enhancing the reliability ofthe tunnel oxide film.

Further, the program potential (program pulse level) is graduallyincreased from a lower value to a higher value. Namely, if the programpotential is gradually increased, the width of the threshold voltagedistribution of the memory cell can be empirically narrowed, comparedwith a case where the initial program potential is set at a high valueand this program potential is gradually decreased.

If the number of times at which a program pulse is supplied to the wordline is, for example, 10 or more, “00” verify read is conducted to thememory cell to which “00”-programming is conducted after a program pulseis supplied to the word line so as to verify whether or not data “00”has been successfully programmed into the memory cell (in steps ST10 toST11).

Further, if the number of times at which a program pulse is supplied tothe word line is, for example, 14 or more, “01” verify read is conductedto the memory cell to which “01”-programming is conducted after aprogram pulse is supplied to the word line so as to verify whether ornot data “01” has been successfully programmed into the memory cell (insteps ST8A to ST9A, ST8B to ST9B).

The data read from the memory cell by the “00” verify read is dataindicating whether or not “00”-programming has been sufficientlyconducted and this data is stored in the latch circuit LATCH1 in a datacircuit existing in a column to which “00”-programming is conducted.

The data read from the memory cell by the “01” verify read is dataindicating whether or not “01”-programming has been sufficientlyconducted and this data is stored in the latch circuit LATCH1 in a datacircuit existing in a column to which “01”-programming is conducted.

Thereafter, simultaneously with an operation of supplying the nextprogram pulse to the word line (in step ST5), an operation (Programcompletion detection) for detecting whether or not “00”-programming or“01”-programming has been sufficiently conducted is executed by aprevious program pulse based on the data in the latch circuit LATCH1 (insteps ST6 to ST7).

To be specific, in the odd page data program operation, as shown in FIG.22, four types of programs, i.e., “11”, “10”, “00” and “01” exist.“11”-programming and “10”-programming are intended to maintain the stateof a memory cell after even page data has been programmed into thememory cell. In addition, “00”-programming means increasing thethreshold voltage by a program pulse and changing the “10” state to “00”state. “01”-programming means increasing the threshold voltage by aprogram pulse and changing the “11” state to the “01” state.

If predetermined data “11”, “10”, “00” or “01” has been sufficientlyprogrammed into all of the selected memory cells (columns) (or,actually, if data “00” or “01” has been sufficiently programmed into thememory cells to which “00” programming or “01”-programming areconducted), then, the odd page data program operation is completed (in astep ST6).

If predetermined data “11”, “10”, “00” or “01” has not been sufficientlyprogrammed into at least on selected memory cell (column) (or actually,data “00” or “01” has not been sufficiently programmed into a memorycell to which “00”-programming or “01”-programming is conducted), “00”verify read, “01” verify read and the supply of a program pulse arecontinued (in steps ST5 to ST11).

Here, in this embodiment, after “00”-programming has been sufficientlyconducted to all the memory cells to which “00”-programming isconducted, “00” verify read is not conducted and only “01” verify readand Program completion detection are conducted (a route of steps ST7,ST8 and ST9B).

The reason for using such a sequence is that “00”-programming is usuallycompleted earlier than “01”-programming (the threshold voltage in the“00” state is lower than that in the “01” state), “00” verify read afterthe completion of “00”-programming is omitted to thereby shorten programtime (accelerate program).

Meanwhile, in this embodiment, the operation (Program completiondetection) for detecting whether or not the program issufficient/deficient is conducted simultaneously with the operation forsupplying a program pulse to the word line. Alternatively, the Programcompletion detection may be conducted right after “00” verify read or“01” verify read and then a program pulse may be supplied again if theresult of the Program completion detection shows that the program isdeficient.

Alternatively, program pulses may not be supplied to the memory cellwhich has been programmed sufficiently and a program pulse iscontinuously supplied (reprogrammed) only to the memory cell which hasbeen programmed deficiently, thereby preventing memory cell having goodprogram characteristics from excessively programmed.

The above description has been given to the outline of the odd page dataprogram operation.

As stated above, the odd page data program operation consists of loadingof even page data stored in a memory cell (Internal data load), thesupply of program pulses, “00” verify read (VERIFY00), “01” verify read(VERIFY01), Program completion detection and “00” program completiondetection.

Now, these operations will be described in this order in detail.

2.-2.-1 “Internal Data Load”

Internal data load is an operation for reading even page data stored ina memory cell and latching the data to the storage circuit (DRAM cell,i.e., node CAP1 ij) in the data circuit. It is noted that program data(odd page data) is temporarily latched by the node CAP2 ij and thenlatched again by the latch circuit LATCH1.

FIGS. 36 and 37 show operation timing relating to Internal data load,respectively.

Internal data load consists of four operations (1st Quarter, 2ndQuarter, 3rd Quarter and 4th Quarter).

The 1st Quarter and the 2nd Quarter are indicated by solid lines inFIGS. 36 and 37, respectively. The 3rd Quarter is almost the same as the1st Quarter except for a portion indicated by two-dot chain lines shownin FIG. 36. The 4th Quarter is almost the same as the 2nd Quarter exceptfor a portion indicated by two-dot chain lines shown in FIG. 37.

2.-2.-1.-1. “Internal Data Load 1st Quarter”

The solid lines of FIG. 36 indicate operation timing relating to theInternal data load 1st Quarter.

If odd page program data inputted externally of the chip is “1”, thelevel of the node Naij of the latch circuit LATCH1 is “H”. If odd pageprogram data inputted externally of the chip is “0”, the level of thenode Naij of the latch circuit LATCH1 is “L”.

While setting the potential (read potential) of a selected word line atVcgr10, a read operation is carried out. In this case, if the memorycell is in the “11” state, the charges of the bit line are dischargedand the level of the bit line becomes “L”. If the memory cell is in the“10” state, the bit line maintains a precharge potential and the levelof the bit line is, therefore, “H”.

In the meantime, while reading the memory cell data to the bit line, theodd page data latched by the latch circuit LATCH1 is transferred to thenode CAP2 ij.

To be specific, if the odd page data is “1”, i.e., the level of the nodeNaij of the latch circuit LATCH1 is “H”, the potential of the node CAP2ij becomes about 4V at period SCLK5. If the odd page data is “0”, i.e.,the level of the node Naij of the latch circuit LATCH1 is “L”, thepotential of the node CAP2 ij becomes Vss at period SCLK5.

Then, the potential of the bit line is sensed and latched by the latchcircuit LATCH1. If the memory cell is in the “11” state, the level ofthe bit line is “L”. Thus, the level of the sense node DTNij becomes “L”and that of the node Naij of the latch circuit LATCH1 becomes “L”, aswell. If the memory cell is in the “10” state, the level of the bit lineis “H”. Thus, the level of the sense node DTNij becomes “H” and that ofthe node Naij of the latch circuit LATCH1 becomes “H”, as well.

Further, at period RCLK5, when the potential of DTG1 becomes Vsg, thedata in the latch circuit LATCH1 is transferred to the DRAM cell, i.e.,the node CAP1 ij and latched thereby.

As can be seen from the above, at a time when the 1st Quarter iscompleted, the odd page data is latched by the node CAP2 ij and the evendata is latched by the node CAP1 ij.

The data of the nodes CAP1 ij and CAP2 ij at the time of completion ofthe 1st Quarter become the data as shown in Table 6.

TABLE 6 Data of capacitor C1, C2 after “Internal Data Load 1st Quarter”“11” “10” “00” “01” CAP1ij “Low” “High” “High” “Low” CAP2ij “High”“High” “Low” “Low”

Namely, in “Internal data load 1st Quarter”, if the even page datastored in the memory cell is “1” (in the “11” state), the level of thenode CAP1 ij becomes “L” and if the even page data stored in the memorycell is “0” (in the “10” state), the level of the node CAP1 ij becomes“H”.

Further, if the odd page data is “1” (the memory cell state “11” or “10”is not changed), the level of the node CAP2 ij becomes “H” and if theodd page data is “0” (the memory cell state is changed to “00” or “01”),the level of the node CAP2 ij becomes “L”.

FIG. 38 shows the simplified movement of even/odd page data in the“Internal data load 1st Quarter”.

2.-2.-1.-2. “Internal Data Load 2nd Quarter”

The solid lines of FIG. 37 indicate operation timing relating to theInternal data load 2nd Quarter.

Following the Internal data load 1st Quarter, the Internal data load 2ndQuarter is started. In the Internal data load 2nd Quarter, an operationfor returning the odd page data latched by the node CAP2 ij to the latchcircuit LATCH1 is conducted.

First, at period ILCLK1, the potential of BLSe becomes Vss and at periodILCLK2, the potential of BLSo becomes Vdd. The potential of BLCRL isVss. As a result, a node Ns shown in FIG. 9 is short-circuited to thenode BLCRL and the potential of the node Ns becomes Vss.

Further, at period ILCLK2, the potentials of SEN and LAT become Vss andthose of SENB, LATB become Vdd, and the latch circuit LATCH1, i.e., theclocked inverters CINV1 and CINV2, is deactivated.

Then, at period ILCKL3, when the potential of nPRST becomes Vss, thesense node DTNij is precharged with Vdd. Further, at period ILCLK4, whenthe potential of nPRST becomes Vdd, the sense node DTNij turns into afloating state.

At period ILCLK3, the potential of BLC becomes Vsg and at period ILCLK5,the potential of BLCLMP becomes Vsense (e.g., about 1.6V). At thismoment, since the potential of the node Ns is Vss, the potential of thesense node DTNij becomes Vss, as well.

Thereafter, at period ILCLK6, the potential of BLCLMP becomes Vss and atperiod ILCLK7, the potential of REG2 becomes Vsg. At this moment, thepotential of the sense node DTNij changes according to the data at thenode CAP2 ij.

For example, as is obvious from Table 6 above, if odd page data is “1”,i.e., “11”-programming and “10”-programming are conducted (to bespecific, memory cell data is maintained, i.e., during write inhibit),the level of the node CAP2 ij is “H”. Due to this, the MOS transistorshown in FIG. 9 is turned on. As a result, the sense node DTNij isconnected to the node COMi and the potential of the sense node becomesVdd.

Meanwhile, if the odd page data is “00”, i.e., “00”-programming and“01”-programming are conducted, the level of CAP2 ij is “L”. Due tothis, the MOS transistor TN1 shown in FIG. 9 is turned off. As a result,the potential of the sense node DTNij remains Vss.

Thereafter, at period ILCLK9, the potential of SEN becomes Vdd and theclocked inverter CINV1 turns into an operation state. Namely, thepotential of the sense node DTNij is sensed by the clocked inverterCINV1. Also, at period ILCLK10, the potential of LAT becomes Vdd and thelatch circuit LATCH1 turns into an operation state.

In other words, the level of the node Naij of the latch circuit LATCH1is “H” if the odd page data is “1” and the potential level thereof is“L” if the latch circuit LATCH1 is “0”.

As a result, the state of the DRAM cell (node CAP1 ij) and that of thenode Naij of the latch circuit LATCH1 at the time of completion of the2nd Quarter become those as shown in Table 7.

TABLE 7 Data of capacitor C1 and latch circuit LATCH1 after “InternalData Load 2nd Quarter” “11” “10” “00” “01” CAP1ij “Low” “High” “High”“Low” Naij “High” “High” “Low” “Low”

It is noted that FIG. 39 shows the simplified movement of the odd pagedata in the “Internal data load 2nd Quarter”.

2.-2.-1.-3. “Internal Data Load 3rd Quarter”

The solid lines of FIG. 36 (two-dot chain lines for SGD and REG1)indicate operation timing relating to the Internal data load 3rdQuarter.

In the Internal data load 3rd Quarter and the Internal data load 4thQuarter, an operation for inverting the data latched by the DRAM cell(node CAP1 ij) in the Internal data load 1st Quarter and the Internaldata load 2nd Quarter (“H”→“L” and “L”→“H”) is carried out.

As shown in Table 7 above, the data latched by the node CAP1 ij is “L”if the even page data is “1” and “H” if the even page data is “0”.Namely, if “1” and “0” are regarded as “H” and “L”, respectively, thevalue of the even page data is opposite to the value of the data latchedby the node CAP1 ij.

Then, in the Internal data load 3rd Quarter and the Internal data load4th Quarter, the data latched by the DRAM cell (node CAP1 ij) isinverted so that the value of the even page data becomes the same as thevalue of the data latched by the node CAP1 ij.

The differences of the Internal data load 3rd Quarter from the Internaldata load 1st Quarter are {circle around (1)} the potential of SGD isVss; and {circle around (2)} during periods RCLK7 to RCLK8, thepotential of REG1 becomes Vdd.

In the Internal data load 3rd Quarter, after the data at the node CAP1ij is inverted and transferred to the sense node DTNij, the odd pagedata latched by the latch circuit LATCH1 is transferred to the node CAP2ij and then the data at the sense node DTNij is transferred to the latchcircuit LATCH1.

First, as in the case of the Internal data load 1st Quarter, at periodRCLK4, the bit line is precharged and the potential of the bit linebecomes about 0.8V. Then, at period RCLK7, the potential of SGS becomesVread. In this embodiment, however, since the potential of SGD is alwaysVss, the charges of the bit line are not discharged through the memorycell.

In this embodiment, at period RCLK7, when the potential of REG1 becomesVdd, it is determined whether to discharge the charges of the bit line(or sense node) or to maintain the present state based on the datalatched by the CAP1 ij.

For example, as is obvious from Table 7 above, if the even page data is“0”, i.e., “10”-programming or “00”-programming is conducted, thepotential of the node CAP1 ij is Vdd. Due to this, the MOS transistorTN3 (FIG. 9) is turned on and the bit line (sense node) isshort-circuited to VREG (Vss).

On the other hand, if the even page data is “1”, i.e., “11”-programmingor “01”-programming is conducted, the potential of the node CAP1 ij isVss. Due to this, the MOS transistor TN3 (FIG. 9) is turned off and thebit line (sense node) maintains the precharge potential (about 0.8V).

Thereafter, the odd page data latched by the latch circuit LATCH1 istransferred to the node CAP2 ij at period SCLK2 as in the case of theInternal data load 1st Quarter. Following this, at period SCLK6, thelevels of both SEN and LAT become “L” and the latch circuit LATCH1 turnsinto a non-operation state.

Further, at period SCLK7, the potential of BLC becomes Vsg and that ofnPRST becomes Vss. At period SCLK8, the potential of nPRST becomes Vdd.At period SCLK9, the potential of BLCLMP becomes Vsense and at periodSCLK13, the level of SEN becomes “H” and the potential of the sense nodeDTNij is sensed by the clocked inverter CINV1. Also, at period SCLK14,the level of LAT becomes “H” and the latch circuit LATCH1 turns into anoperation state.

As a result, if the even page data is “0” (the potential of the nodeCAPij is Vdd), the level of the node Naij of the latch circuit LATCH1becomes “L”. if the even page data is “1” (the potential of the nodeCAPij is Vss), the level of the node Naij of the latch circuit LATCH1becomes “H”.

Thereafter, at period SCLK15, if the potential of DTG1 is set at Vsg,the data in the latch circuit LATCH1 is transferred to the DRAM cell(node CAP1 ij).

Here, if the even page data is “0” (the potential of the node CAP1 ij isVdd), the level of the node Naij of the latch circuit LATCH1 is “L”. Dueto this, the node CAP1 ij is inverted from Vdd (“H”) to Vss (“L”).Further, if the even page data is “1” (the potential of the node CAP1 ijis Vss), the level of the node Naij of the latch circuit LATCH1 is “H”.Due to this, the node CAP1 ij is inverted from Vss (“L”) to Vdd (“H”).

At the time of the completion of the Internal data load 3rd Quarter, theodd page data has been stored in the node CAP2 ij and the even page datahas been stored in node CAP1 ij.

The data of CAP1 ij and CAP2 ij at the time of the completion of the 3rdQuarter are those as shown in Table 8.

TABLE 8 Data of capacitor C1, C2 after “Internal Data Load 3rd Quarter”“11” “10” “00” “01” CAP1ij “High” “Low” “Low” “High” CAP2ij “High”“High” “Low” “Low”

FIG. 40 shows the simplified movement of even/odd page data in the“Internal data load 3rd Quarter”.

2.-2.-1.-4. “Internal Data Load 4th Quarter”

The solid lines of FIG. 37 (two-dot chain lines for SGD) show operationtiming relating to the Internal data load 4th Quarter.

In the Internal data load 4th Quarter, an operation for returning theodd page data latched by the node CAP2 ij to the latch circuit LATCH1 iscarried out.

The Internal data load 4th Quarter differs from the Internal data load2nd Quarter only in that the potential of SGD is always Vss.

The operation for returning the odd page data latched by the node CAP2ij to the latch circuit LATCH1 is the same as that in the Internal dataload 2nd Quarter. Therefore, the detailed description of the Internaldata load 4th Quarter will not be given herein.

The data latched by the DRAM cell (node CAP1 ij) and the latch circuitLATCH1 (node Naij) are those as shown in Table 9.

TABLE 9 Data of capacitor C1 and latch circuit LATCH1 after “InternalData Load 4th Quarter” “11” “10” “00” “01” CAP1ij “High” “Low” “Low”“High” Naij “High” “High” “Low” “Low”

FIG. 41 shows the simplified movement of odd page data in the “Internaldata load 4th Quarter”.

The Internal data load (1st Quarter, 2nd Quarter, 3rd Quarter and 4thQuarter) has been described above. As a result of the Internal dataload, the odd page data is latched by the latch circuit LATCH1 and theeven page data is latched by the DRAM cell (node CAP1 ij). Besides, thevalues of the odd/even page data are the same as those of the latcheddata (“1” corresponds to “H” and “0” corresponds to “L”).

Thereafter, as shown in Table 9, based on the two-bit data latched bythe CAP1 ij and Naij, the actual program operation of the odd page datais carried out.

2.-2.-2. Supply of Program Pulse

A program pulse is supplied exactly at the same timing as that forsupplying a program pulse for the even page data.

In “00”-programming and “01”-programming, the level of the node Naij ofthe latch circuit LATCH1 is “L” as shown in Table 9 and the potential ofthe bit line becomes, therefore, Vss. Accordingly, a high electric fieldis applied to the tunnel oxide film of a selected memory cell andelectrons are injected into the floating gate electrode of the memorycell by the FN tunnel effect, thereby effecting the program.

In “11”-programming and “10”-programming, the potential level of thenode Naij of the latch circuit LATCH1 is “H” as shown in Table 9 above,the potential of the bit line becomes Vd. Accordingly, a high electricfield is not applied to the tunnel oxide film of the selected memorycell and the state of the memory cell does not change (i.e., the memorycell is maintained in either the “11” state or the “10” state).

Operation timing relating to the supply of a program pulse is the sameas that relating to the supply of a program pulse (section 2.-1.-1) inthe even page data program operation (section 2.-1), which detaileddescription will not be, therefore, given herein.

2.-2.-3. “VERIFY01”

FIG. 42 shows operation timing for “01” verify read.

In “0” verify read (VERIFY01), after the bit line is precharged, thepotential of the selected word line is set at Vcgv01 (e.g., about 1.75V)shown in FIG. 20, the potential change of the bit line is detected andmemory cell data is read.

In “VERIFY01”, if two storage circuits (LATCH1, C1) in the data circuitlatch program data of “11”, “10” and “00”, the program data has nochange.

As for data “00”, if “VERIFY00”, which will be described later, is OK(program is sufficient), the data changes from “00” to “11”. As forthis, reference is made to “VERIFY00” described later. However, thevalue of the data, whether “00” or “10”, does not change in “VERIFY01”.

On the other hand, in “VERIFY01”, if the two storage circuits (LATCH1,C1) in the data circuit latch program data of “01” and read dataindicates sufficient program, i.e., the level of the bit line is “H”,then the program is not conducted thereafter and the program datachanges from “01” to “11” (odd page data changes from “0” to “1”).

Further, in “VERIFY01”, if the two storage circuits (LATCH1, C1) in thedata circuit latch the program data of “01” and the read data indicatesthat program is deficient, i.e., the level of the bit line is “L”, thenthe program is continuously conducted and the program data has nochange.

The concrete operation will be described as follows.

First, while the bit line is being precharged or discharged (cell datais being read), the program data stored in the latch circuit LATCH1 istransferred to the node CAP2 ij and temporarily stored in the node CAP2ij. By doing so, the read data is prevented from colliding against theodd page data.

At period RCLK1, the potentials of CAPCRG and VREG are set at Vdd and atperiod RCLK4, the potential of BOOT is set at Vss. At period RCLK5, whenthe potential of VREG becomes Vss, the node CAP2 ij is reset at Vss.During this time, the potential of DTG2 is Vss.

At period RCLK9/SCLK1, the potential of CAPCR becomes Vss and the nodeCAP2 ij turns into a floating state. Then, at period SCLK2, thepotential of DTG2 becomes Vsg (e.g., about 4.5V) and the program data(odd page data) latched by the latch circuit LATCH1 is transferred tothe node CAP2 ij by way of the MOS transistor TN2 and temporarily storedin the node CAP2 ij.

Namely, if the odd page program data is. “0” (“00”-programming or“01”-programming is conducted), the level of the node Naij of the latchcircuit LATCH1 is “L” and the potential of the node CAP2 ij, therefore,becomes Vss.

Further, if the odd page program data is “1” (the memory cell ismaintained in the “11” or “10” state and “00”-programming and“01”-programming are sufficient), then the level of the node Naij of thelatch circuit LATCH1 is “H” and the potential of the node CAP2 ij,therefore, becomes Vdd.

Then, at period SCLK3, the potential of DTG2 becomes Vdd and at periodSCLK4, the potential of BOOT becomes Vdd.

At this moment, if the odd page program data is “0” (“00”-programming or“01”-programming is conducted), the potential of the node CAP2 ijremains Vss. Also, if the odd page data is “1” (the memory cell ismaintained in the “11” or “10” state) and the potential of the node CAP2ij is booted by the capacitor DLN (C2) and, therefore, rises from Vdd(e.g., about 2.3V) to about 3.5V.

Thereafter, at period SCLK5, the potential of DTG2 becomes Vss and thenode CAP2 ij is electrically disconnected from the latch circuit LATCH1.

Simultaneously with the above-stated operation, a bit line prechargeoperation and an operation for reading the memory cell data to the bitline are carried out.

That is, after the bit line is precharged, the potential of SGS becomesVread at period RCLK7 and the potential of the bit line changesaccording to the memory cell data.

For example, the memory cells (cell to which “11” or “10”-programming isconducted (i.e., cell which is not programmed) and cell to which“01”-programming is conducted) other than the memory cells to which“01”-programming is conducted, are turned on by the potential Vcgv01(e.g., about 1.75V). Thus, the charges of the bit line are dischargedand the bit line has a potential not higher than 0.3V.

Further, in case of the memory cell to which “01”-programming isconducted, if “01”-programming is deficient, the memory cell is turnedon by the potential Vcgv01 (e.g., about 1.75V). Thus, the charges of thebit line are discharged and the bit line has a potential not higher than0.3V.

Further, in case of the memory cell to which “01”-programming isconducted, if “01”-programming is sufficient, the memory cell is turnedoff by the potential Vcg01 (e.g., about 1.75V). Thus, the charges of thebit line are not discharged and the bit line maintains the potential0.8V.

Thereafter, at period SCLK6, the levels of both SEN and LAT become “L”,those of both SEN and LATB become “H”, and the latch circuit LATCH1 inthe data circuit, i.e., the clocked inverters CINV1 and CINV2, turnsinto a non-operation state.

Further, at period SCLK7, the potential of BLC becomes Vsg (e.g., about4.5V) and the level of the nPRST becomes “L”. The sense node DTNij isthereby charged and the potential of the sense node becomes Vdd. At thesame time, the potential of the node Naij becomes Vdd. At period SCLK8,when the potential of nPRST becomes Vdd, the sense node DTNij turns intoa floating state.

At period SCLK9, when the potential of BLCLMP becomes Vsense (e.g.,about 1.6V), the memory cell data read to the bit line is transferred tothe sense node DTNij.

Namely, in case of each of the memory cells which have been programmedsufficiently among the memory cells to which “11” or “10”-programming isconducted, those to which “00”-programming is conducted and those towhich “01”-programming is conducted, the potential of the bit linebecomes not higher than 0.3V. Due to this, the potential of the sensenode DTNij decreases to not higher than 0.3V, as well.

Meanwhile, as for each of the memory cells which have been programmedsufficiently among the memory cells to which “01-”-programming isconducted, the potential of the bit line is maintained 0.8V. Due tothis, the clamping MOS transistor TN9 is cut off and the sense nodeDTNij maintains the potential Vdd.

At period SCLK10, the potentials of the sense node DTNij become those asshow in Table 10.

TABLE 10 Sense node (DTNij·Naij) in “VERIFY 01” “11”, “10”- “00”- “00”-“01”- “01”- programming programming programming programming programming(Write inhibit) Deficient Sufficient Deficient Sufficient Point of “Low”“Low” “Low” “Low” “High” SCLK 10 Point of “High” “Low” “Low” “Low”“High” SCLK 12

Thereafter, at period SCLK11, the potential of REG2 becomes Vsg and theMOS transistor TN6 (FIG. 9) is turned on.

Here, in case of conducting “11”-programming and “10”-programming (oddpage data is “1”), “H” is stored in the node CAP2 ij and the MOStransistor TN1 (FIG. 9) is, therefore, turned on. That is, the COMi (setat Vdd) and the sense node DTNij are short-circuited to each other, withthe result that the potential of the sense node DTNij becomes Vdd.

Further, in case of conducting “00”-programming and “01”-programming(odd page data is “0”), “L” is stored in the node CAP2 ij and the MOStransistor TN1 (FIG. 9) is, therefore, turned off. That is, the COMi(set at Vdd) and the sense node DTNij are electrically disconnected fromeach other, with the result that the potential of the sense node DTNijhas no change.

Accordingly, the potentials of the sense node DTNj at period SCLK12become those as shown in Table 10 above.

Thereafter, at period SCLK13, the potential of SEN becomes Vdd, that ofSENB becomes Vss and the clocked inverter CINV1 turns into an operationstate, whereby the potential of the sense node DTNij is sensed.

As shown in Table 10 above, in case of “11”-programming and“10”-programming, the level of the sense node DTNij is “H” and that ofthe node Naij is “H”. The level of the node Naij is originally “H” (seeTable 9) in case of conducting “11”-programming and “10”-programming(odd page data is “1”). In case of conducting “11”-programming and“10”-programming, therefore, the program data has no change.

Further, in case of conducting “00”-programming, the level of the sensenode DTNij is “L” and that of the node Naij is “L”, as well. Since thelevel of the node Naij is originally “L” (see Table) in case ofconducting “00”-programming (odd page data is “0”), the program data hasno change in case of conducting “00”-programming.

As for “00”-programming, in “VERIFY00” to be described later, if dataindicating that program has been conducted sufficiently is read, datachanges from “00” to “10” (odd page data changes from “0” to “1”).However, in “VERIFY01”, the program data (“00” or “10”) has no change.

Further, if “01”-programming is conducted and the “01”-programming isdeficient, the level of the sense node DTNij is “L” and that of the nodeNaij is “L”, as well. Since the level of the node Naij is originally “L”(see Table 9) in case of conducting “01”-programming (odd page data is“0”), the program data has no change even if “01”-programming isconducted and the program is deficient.

Further, if “01”-programming is conducted and the “01”-programming isdeficient, the level of the sense node DTNij is “H” and that of the nodeNaij is “H”, as well. Since the level of the node Naij is “L” (see Table9) in case of conducting “01”-programming (odd page data is “0”), theprogram data changes from “01” to “11” (the value of the node Naij ofthe latch circuit LATCH1, i.e., the odd page data changes from “0” to“1”) if “0”-programming is conducted and the program is sufficient.

FIG. 43 shows the simplified state of “01” verify read operation.

2.-2.-4. “VERIFY00”

FIG. 44 shows operation timing for “00” verify read.

In “00” verify read (VERIFY00), after the bit line is precharged, thepotential of a selected word line is set at Vcgv00 (e.g., about 0.9V),the potential change of the bit line is detected and memory cell data isread.

In “VERIFY00”, if the two storage circuits (LATCH1, C1) in the datacircuit latch program data of “11”, “10” and “01”, the program data haveno change.

On the other hand, in “VERIFY00”, if the two storage circuits (LATCH1,C1) in the data circuit latch program data of “00” and the read dataindicates that the program i-s—sufficient, i.e., the level of the bitline is “H”, then the program data changes from “00” to “10” (odd pagedata changes from “0” to “1”) so that the program is not conductedthereafter.

In “VERIFY00”, if the two storage circuits (LATCH1, C1) in the datacircuit latch program data of “00” and the read data indicates that theprogram is insufficient, i.e., the level of the bit line is “L”, thenthe program data has no change so as to continue the program operation.

As shown in the flow chart of FIG. 30, “VERIFY01” described above isexecuted prior to the “VERIFY00”.

Accordingly, in “VERIFY01”, the data indicating that “01”-programming issufficient has been read, the data latched by the two storage circuits(LATCH1, C1) in the data circuit have already changed from “01” to “11”.If data indicating that “01”-programming is insufficient is read, thedata latched by the two storage circuits (LATCH1, C1) in the datacircuit remains “01”.

The concrete operation will be described hereinafter.

First, an operation for precharging the bit line and an operation forreading memory cell data to the bit line are executed.

Namely, after precharging the bit line, at period RCLK7, the potentialof SGS becomes Vread and the potential of the bit line changes accordingto the memory cell data.

For example, the memory cells to which “11”-programming and“10”-programming are conducted (i.e., memory cells which are notprogrammed), are turned on by the potential Vcgv00 (e.g., about 0.9V).Due to this, the charges of the bit line are discharged and thepotential of the bit line becomes not higher than 0.3V.

Further, in case of the memory cells to which “00”-programming isconducted, if the “00”-programming is deficient, the memory cell isturned on by the potential Vcgv00 (e.g., about 0.9V). Due to this, thecharges of the bit line are discharged and the potential of the bit linebecomes not higher than 0.3V.

Moreover, in case of the memory cells to which “00”-programming isconducted, if the “00”-programming is sufficient, the memory cell isturned off by the potential Vcgv00 (e.g., about 0.9V). Due to this, thecharges of the bit line are not discharged and the bit line maintainsthe potential 0.8V.

Moreover, in case of the memory cells to which “01”-programming isconducted, if the “01”-programming is sufficient, the memory cell isturned off by the potential Vcgv00 (e.g., about 0.9V). Due to this, thecharges of the bit line are not discharged and the bit line maintainsthe potential 0.8V.

However, if “01”-programming is deficient, there are cases where thememory cell is turned on (the threshold voltage is lower than Vcgv0) andcases where the memory cell is turned off (the threshold voltage ishigher than Vcgv00). Due to this, if “01”-programming is deficient, itis determined whether the bit line maintains the potential 0.8V or has apotential not higher than 0.3V according to the threshold voltage of thememory cell.

Here, in this embodiment, while the memory cell data is being read tothe bit line, i.e., at periods RCLK7 to RCLK8, the level of REG1 becomes“H”. It is noted that the potential of BLCLMP is Vclmp (e.g., about1.6V).

As is obvious from Table 9, when the even page data is “1”(“11”-programming and “01”-programming), the DRAM cell (node CAP1 ij)latches “H”. Namely, in case of “11”-programming and “01”-programming,the sense node DTNij is short-circuited to VREG (Vss) and the potentialof the sense node is forcedly set at Vss.

As a result, if “11”-programming and “10”-programming are conduced,“00”-programming is deficient and “01”-programming is conducted, thelevel of the bit line becomes “L”, i.e., becomes a potential not higherthan 0.3V. Only if “00”-programming is sufficient, the bit linemaintains the level “H”, i.e., the potential 0.8V.

Thereafter, at period RCLK9, the potential of BLCLMP becomes Vss and thebit line is electrically disconnected from the sense node.

In the meantime, while the above-stated operations, i.e., the bit lineis being precharged or discharged (cell data is being read), the programdata stored in the latch circuit LATCH1 is transferred to andtemporarily stored by the node CAP2 ij. By doing so, read data isprevented from colliding against the odd page data.

At period RCLK1, the potentials of CAPCRG and VREG are set at Vdd. Atperiod RCLK4, the potential of BOOT is set at Vss. At period RCLK5, whenthe potential of VREG becomes Vss, the node CAP2 ij is reset at Vss.During these periods, the potential of DTG2 is Vss.

At period RCLK9/SCLK1, the potential of CAPCRG becomes Vss and the nodeCAP2 ij turns into a floating state. Then, at period SCLK2, thepotential of DTG2 becomes Vsg (e.g., about 4.5V) and the program data(odd page data) latched by the latch circuit LATCH1 is transferred toand temporarily stored in the node CAP2 ij by way of the MOS transistorTN2.

That is to say, if the odd page program data is “0” (“00”-programmingand “01”-programming is conducted), the level of the node Naij of thelatch circuit LATCH1 is “L” and the potential of the node CAP2 ij,therefore, becomes Vss.

Further, if the odd page program data is “1” (the “11” or “10” state ismaintained or “00”-programming and “01”-programming are sufficient), thelevel of the node Naij of the latch circuit LATCH1 is “H” and thepotential of the node CAP2 ij, therefore, becomes Vdd.

Thereafter, at period SCLK3, the potential of DTG2 becomes Vdd. Atperiod SCLK4, the potential of BOOT becomes Vdd.

At this time, if the odd page program data is “0” (“00”-programming or“01”-programming is conducted), the potential of the node CAP2 ijremains Vss. If the odd page program data is “1” (the “11” state or “10”state is maintained), the potential of the node CAP2 ij is booted by thecapacitor DLN (C2) and, therefore, rises from Vdd (e.g., about 2.3V) toabout 3.5V.

Then, at period SCLK5, the potential of DTG2 becomes Vss and the nodeCAP2 ij is electrically disconnected from the latch circuit LATCH1.

Further, at period SCLK6, the levels of both SEN and LAT become “L”,those of both SENB and LATB become “H” and the latch circuit LATCH1 inthe data circuit, i.e., the clocked inverters CINV1 and CINV2, turnsinto a non-operation state.

At period SCLK7, the potential of BLC becomes Vsg (e.g., about 4.5V) andthat of nPRST becomes “L”, whereby the sense node DTNij is charged andthe potential of the sense node becomes Vdd. At the same time, thepotential of Naij becomes Vdd. At period SCLK8, when the potential ofnPRST becomes Vdd, the sense node DTNij turns into a floating state.

At period SCLK9, when the potential of BLCLMP becomes Vsense (e.g.,about 1.6V), the memory cell data read to the bit line is transferred tothe sense node DTNij.

Namely, in case of the memory cells which have been programmeddeficiently among those to which “11”-programming and “10”-programmingare conducted and those to which “00”-programming is conducted, thepotential of the bit line is not higher than 0.3V. Due to this, thepotential of the sense node DTNij decreases to a potential not higherthan 0.3V, as well.

On the other hand, in case of the memory cells which have beenprogrammed sufficiently among those to which “00”-programming isconducted, the bit line maintains the potential 0.8V. Due to this, theclamping MOS transistor TN9 (FIG. 9) is cut off and the sense node DTNijmaintains the potential Vdd.

At period SCLK10, the potentials of the sense node DTNij become those asshown in Table 11.

TABLE 11 Sense node (DTNij·Naij) in “VERIFY 00” “11”, “10”- “00”- “00”-“01”- “01”- programming programming programming programming programming(Write inhibit) Deficient Sufficient Deficient Sufficient Point of “Low”“Low” “High” “Low” “Low” SCLK 10 Point of “High” “Low” “High” “Low”“High” SCLK 12

Thereafter, at period SCLK11, the potential of REG2 becomes Vsg and theMOS transistor TN6 (FIG. 9) is turned on.

Here, if “11”-programming and “10”-programming are conducted and“01”-programming is sufficient (odd page data is “1”, note that if“01”-programming is sufficient, “01” is changed to “11”), the node CAP2ij latches “H” and the MOS transistor TN1 (FIG. 9) is, therefore, turnedon. Namely, the COMi (set at Vdd) and the sense node DTNij areshort-circuited to each other, with the result that the potential of thesense node DTNij becomes Vdd.

Further, if “00”-programming is conducted and “01”-programming isdeficient (odd page data is “0”), the node CAP2 ij latches “L” and theMOS transistor TN1 (FIG. 9) is, therefore, turned off. Namely, since theCMOi (having a potential set at Vdd) and the sense node DTNij areelectrically disconnected from each other, the potential of sense nodeDTNij has no change.

Accordingly, the potentials of the sense node DTNij at period SCLK12become those as shown in Table 11.

Then, at period SCLK13, the potential of SEN becomes Vdd, that of SENBbecomes Vss and the clocked inverter CINV1 turns into an operationstate. Due to this, the potential of the sense node DTNij is sensed.

As shown in Table 11 above, if “11”-programming and “10”-programming areconducted, the level of the sense node DTNij is “H” and that of the nodeNaij is “H”, as well. In case of conducting “11”-programming and“10”-programming, the level of the node Naij is originally “H” (seeTable 9). Therefore, if “11”-programming and “10”-programming isconducted, the program data has no change.

Furthermore, if “00”-programming is conducted and the “00”-programmingis deficient, the level of the sense node DTNij is “L” and that of thenode Naij is “L”, as well. In case of conducting “00”-programming (oddpage data “0”), the level of the node Naij is originally “L” (see Table9). Therefore, if “00”-programming is conducted and the “00”-programmingis deficient, the program data has no change, either.

Moreover, if “00”-programming is conducted and the “00”-programming issufficient, the level of the sense node DTNij is “H” and that of thenode Naij is “H”, as well. In case of conducting “00”-programming (oddpage data “0”), the level of the node Naij is originally “L” (see Table9). Therefore, if “00”-programming is conducted and the “00”-programmingis sufficient, the program data changes from “00” to “10” (the value ofthe node Naij of the latch circuit LATCH1, i.e., the odd page datachanges from “0” to “1”).

In addition, if “01”-programming is conducted and the program isdeficient in VERIFY01, the level of the sense node DTNij is “L” and thatof the node Naij is “L”, as well. In case of conducting “01”-programming(odd page data “0”), the level of the node Naij is originally “L” (seeTable 9). Therefore, if “01”-programming is conducted and the program isdeficient, the program data has no change.

If “01”-programming is conducted and the program is sufficient inVERIFY01, the level of the sense node DTNij is “H” and that of the nodeNaij is “H”, as well. If the program is sufficient in VERIFY01, theprogram data changes from “01” to “11” as described above, and the levelof the node Naij is, therefore, “H” (see Table 10). Thus, if“01”-programming is conducted and the program is sufficient, the programdata has no change, either (note: the program data remains “11”).

FIG. 45 shows the simplified state of the “00” verify read operation.

2.-2.-5. “Program Completion Detection”

Following “VERIFY01” and “VERIFY00”, “Program completion detection”operation is carried out to detect whether or not “01”-programming or“00”-programming has been successfully completed to all the memory cellsto which “01”-programming or “00”-programming is conducted.

This detection is made based on the data (see Tables 10 and 11) latchedby the latch circuit LATCH1 in “VERIFY01” and “VERIFY00”. If“01”-programming or “00”-programming is deficient, reprogram (supply ofa program pulse) is executed. If “01”-programming or “00”-programming issufficient, the program (supply of a program pulse) is completed.

FIG. 33 shows operation timing for “Program completion detection”.

As already described in the outline of the operation with reference toFIG. 35, after the completion of “VERIFY00”, the next “supply of aprogramming pulse” is instantly carried out and “Program completiondetection” is executed in parallel with the “supply of a programmingpulse”.

Accordingly, period PCLK7/CCLK1 is the same as period PCLK7/CCLK1 shownin FIG. 29.

Further, in “Program completion detection” in the odd page data programoperation”, operations from periods PCLK7/CCLK1 to CCLK9 shown in FIG.33 are executed.

First, at period CCLK1, the potential of CAPCRG becomes Vsg, that ofVREG becomes Vdd, the node CAP2 ij is charged and the potential of thenode CAP2 ij becomes Vdd (while the potential of DTG2 is Vss).

Then, at period CCLK2 (DCLK1), when the potential of COMHn (FIG. 12)changes from Vss to Vdd and that of NCOML (FIG. 12) changes from Vdd toVss, the potentials of both COMi1 and COMi2 become Vdd and COMi1 andCOMi2 turn into a floating state, and the potential of NCOM becomes Vssand NCOM turns into a floating state.

At period DCLK2, the potential of, for example, REG2-0 becomes Vdd. Atthis time, in FIG. 12, the first and fifth data circuits are selectedand the potentials of REG2 in the first data circuit and that of REG2 inthe fifth data circuit become Vdd.

If the level of the data of the node Naij of the latch circuit LATCH1 is“H (Vdd)” (see Table 11) in each of the first and fifth data circuits,i.e., “11”-programming and “10”-programming (write inhibit) areconducted or “00”-programming and “10”-programming are sufficient, thenthe sense node DTNij maintains “H (Vdd)”. Due to this, the MOStransistor TN6 (FIG. 9) is turned off and COMi1 and COMi2 maintain thepotential Vdd. NCOM, therefore, maintains the potential Vss.

On the other hand, if the level of the data of the node Naij of thelatch circuit LATCH1 is “L (Vss”) (see Table 11) in at least one of thefirst and fifth data circuits, i.e., “00”-programming and“01”-programming is deficient, then the sense node DTNij maintains “L(Vss)”. Due to this, the MOS transistor TN6 (FIG. 9) is turned on andthe potential of COMi1 or COMi2 changes from Vdd to Vss. The potentialof NCOM, therefore, changes from Vss to Vdd.

Likewise, the potentials of REG2-1, REG2-2 and REG2-3 sequentiallybecome Vdd. Namely, when the potential of REG2-1 is Vdd, the second andsixth data circuits are selected. When the potential of REG2-2 is Vdd,the third and seventh data circuits are selected. When the potential ofREG2-3 is Vdd, the fourth and eighth data circuits are selected. In eachdata circuit, the state of the latch circuit LATCH1, i.e., whether“00”-programming and “01”-programming are sufficient/deficient isdetected.

As a result, if data indicating that “11”-programming and“10”-programming (write inhibit) are conducted or “00”-programming and“01”-programming are sufficient, is outputted from all of the first toeighth data circuits, the potential of NCOM becomes Vss at period CCLK3.If data indicating that “00”-programming and “01”-programming aredeficient, is outputted from at least one of the first to eighth datacircuits, the potential of NCOM becomes Vdd at period CCLK3.

Further, all columns are connected in series to the FLAG node (FIG. 12).Accordingly, the FLAG node is preset to have the potential Vdd and in afloating state and then at period CCLK3, the potential of COLPRE is setat Vdd and the MOS transistor TN17 (FIG. 12) is turned on.

At this time, data indicating that “11”-programming and “10”-programming(write inhibit) are conducted or “00”-programming and “01”-programmingare deficient, is outputted from all data circuits corresponding to allcolumns, the potential of NCOM is Vss and the MOS transistor TN16 (FIG.12) is, therefore, turned off. Accordingly, the FLAG node maintains thepotential Vdd.

Further, if data indicating that “00”-programming and “01”-programmingare deficient is outputted from at least one of all data circuitscorresponding to all columns, the potential of NCOM becomes Vdd and theMOS transistor TN16 (FIG. 12) is, therefore, turned on. Accordingly, thepotential of the FLAG node changes from Vdd to Vss.

As can be seen from the above, only if there does not exist a memorycell for which “00”-programming and “01”-programming are deficient ineach column, the FLAG node maintains the potential Vdd. If there existsa memory cell for which “00”-programming and “01”-programming aredeficient, in at least one column, the potential of the FLAG nodebecomes Vss.

Accordingly, if this FLAG node level is detected and the potential ofthe FLAG node is Vdd, i.e., there does not exist a column (memory cell)for which “00”-programming and “01”-programming are deficient, the oddpage data program routine is completed. If the potential of the FLAGnode is Vss, i.e., there exists at least one column (memory cell) forwhich “00”-programming and “01”-programming are deficient, the “01”verify read operation and the “00” verify read operation are re-executedand then Program completion detection is conducted in parallel with thesupply of a program pulse.

In a fail column replaced by a spare cell by the redundancy circuit dueto the presence of a fail cell (it is assumed that a replacement unit iseight columns), the fuse element of the batch detection circuit 10 shownin FIG. 12 is cut off. Accordingly, the potential of the FLAG node doesnot become Vss because of such a fail column.

2.-2.-6. ““00”-Program Completion Detection”

After Program completion detection, “00”-Program completion detection isconducted to detect whether or not “00”-programming has beensuccessfully completed to all the memory cells to which “00”-programmingis conducted.

The purpose of “00”-Program completion detection is, as alreadydescribed in the outline of the odd page data program operation, to omit“VERIFY00” after all the memory cells to which “00”-programming isconducted have been sufficiently programmed and finally to make all thememory cells to which “00”-programming and “01”-programming areconducted, sufficiently programmed.

In that case, after all the memory cells to which “00”-programming isconducted have been programmed sufficiently, “VERIFY00” is omitted.Thus, it is possible to shorten program time (accelerate program).

Periods CCLK4 to CCLK9 shown in FIG. 33 indicate operation timing for“00”-Program completion detection.

“00”-Program completion detection is conducted in parallel with thesupply of a program pulse (FIG. 29) as in the case of Program completiondetection.

At period CCLK5, the potential of CAPCRG becomes Vsg and the MOStransistor TN4 (FIG. 9) is turned on. As a result, the node CAP2 ij isshort-circuited to VREG (Vdd) and the potential of the node CAP2 ijbecomes Vdd. Then, at period DCLK2, the potential of CAPCRG becomes Vssand the MOS transistor TN4 (FIG. 9) is turned off. As a result, the nodeCAP2 ij turns into a floating state. It is noted that the potential ofDTG2 is Vss.

Thereafter, at period DCLk3, the potential of REG1 becomes Vdd. Inaddition, in case of “11”-programming and “01”-programming, the level ofthe node CAP1 ij is “H” (see Table 9).

In case of “11”-programming, the potential of the sense node DTNij isVdd. Therefore, the MOS transistors TN3 and TN10 (FIG. 9) are turned offand the node CAP2 ij maintains the potential Vdd.

If “01”-programming is sufficient, the potential of the sense node DTNijis Vdd. Therefore, the MOS transistors TN3 and TN10 (FIG. 9) are turnedoff and the node CAP2 ij maintains the potential Vdd. If“01”-programming is deficient, the potential of the sense node DTNij isVss. Therefore, the MOS transistors TN3 and TN10 (FIG. 9) are turned onand the potential of the node CAP2 ij changes from Vdd to Vss.

Further, in case of “00”-programming and “10”-programming, the level ofthe node CAP1 ij is “L” (see Table 9). Therefore, the MOS transistor TN3(FIG. 9) is turned off and the node CAP2 ij maintains the potential Vdd.

Namely, at period DCLK4, only if “01”-programming is deficient, thepotential of the node CAP2 ij becomes Vss; otherwise, the node CAP2 ijmaintains the potential Vdd.

At period DCLK4, the level of COMHn becomes “L” and the potentials ofCOMi1 and COMi2 shown in FIG. 12 have the potential Vdd and turn into afloating state.

It is noted that the node NCOM has the potential Vss and in a floatingstate.

At period DCLK4, the potential of, for example, REG2-0 becomes Vdd. Atthis time, in FIG. 12, the first and fifth data circuits are selectedand the potential of REG2 in the first data circuit and that of REG2 inthe fifth data circuit become Vdd.

Here, COMi1 and COMi2 are discharged (the potentials of COMi1 and COMi2become Vss) only when the potential of the node CAP2 ij is Vdd and thatof the sense node DTNij is Vss. This corresponds to a case where“00”-programming is deficient.

Accordingly, if “00”-programming is deficient in at least one of thefirst and fifth data circuits, the potential of at least one of COMi1and COMi2 becomes Vss and at least one of the MOS transistors TP2 andTP3 is turned on. As a result, the node NCOM is charged and thepotential of the node NCOM, therefore, becomes Vdd.

If “00”-programming is not deficient in each of the first and fifth datacircuits, both COMi1 and COMi2 maintain the potential Vdd and both theMOS transistors TP2 and TP3 are turned off. As a result, the node NCOMmaintains the potential Vss.

Likewise, the potentials of REG2-1, REG2-2 and REG2-3 sequentiallybecome Vdd. Namely, when the potential of REG2-1 is Vdd, the second andsixth data circuits are selected. When the potential of REG2-2 is Vdd,the third and seventh data circuits are selected. When the potential ofREG2-3 is Vdd, the fourth and eighth data circuits are selected. In eachdata circuit, whether “00”-programming is sufficient/deficient isdetected.

As a result, if data indicating that “00”-programming is deficient, isoutputted from at least one of the first to eighth data circuits, thepotential of NCOM becomes Vdd at period CCLK7.

Further, only if data indicating that “00”-programming is deficient, isnot outputted from any one of the first to the eighth data circuits, thepotential of the node NCOM becomes Vss at period CCLK7.

In the meantime, all columns are connected in series to the FLAG node(FIG. 12). Accordingly, the FLAG node is set to have the potential Vddand in a floating state and then at period CCLK7, the potential ofCOLPRE is set at Vdd and the MOS transistor TN17 (FIG. 12) is turned on.

At this time, if data indicating that “00”-programming is deficient, isoutputted from at least one of all data circuits corresponding to allcolumns, the potential of NCOM is Vdd and the MOS transistor TN16 (FIG.12) is, therefore, turned on. Accordingly, the potential of the FLAGnode becomes Vss.

On the other hand, if data indicating that “00”-programming isdeficient, is not outputted from any one of all data circuitscorresponding to all columns, the potential of NCOM is Vss and the MOStransistor TN16 (FIG. 12) is, therefore, turned off. Accordingly, thepotential of the FLAG node becomes Vdd.

As can be seen from the above, only if there does not exist a memorycell for which “00”-programming is deficient in any column, the FLAGnode maintains the potential Vdd. If there exists a memory cell forwhich “00”-programming is deficient in at least one column, thepotential of the FLAG node becomes Vss.

Accordingly, if the level of this FLAG node is detected and thepotential of the FLAG node is Vdd, i.e., there does not exist a column(memory cell) for which “00”-programming is deficient, “VERIFY00” is notconducted thereafter. If the potential of the FLAG node is Vss, i.e.,there exists a column (memory cell) for which “00”-programming isdeficient, “VERIFY00” continues.

In a fail column replaced by a spare cell by the redundancy circuit dueto the presence of a fail cell (it is assumed that a replacement unit iseight columns), the fuse element of the batch detection circuit 10 shownin FIG. 12 is cut off. Accordingly, the potential of the FLAG node doesnot become Vss because of such a fail column.

3. Erase Operation

During the erase operation, an erase Vera (e.g., about 20V) is appliedto the cell well.

The potential of all word lines in a selected memory block are set atthe ground potential Vss. As a result, a high electric field is appliedto the tunnel oxide film of each memory cell in the selected memory cellblock and electrons in the floating gate electrode of the memory cellare emitted to the channel (cell well) and the threshold voltage of thememory cell decreases.

The potentials of all word lines in unselected memory cell blocks areset in a floating state. As a result, if the erase potential Vera isapplied to the cell well, the potential of each word line rises to theerase potential Vera or a potential close to Vera by the capacitivecoupling between the cell well and the word line (control gateelectrode). Therefore, a high electric field is not applied to thetunnel oxide film of each memory cell in the unselected memory cellblocks and the transfer of electrons into the floating gate electrode ofthe memory cell is little and the threshold voltage of the memory celldoes not change.

Meanwhile, in the first memory cell block shown in FIG. 14, a Row shieldline exists on the memory cell array. During the erase operation, thepotential of this Row shield line rises from Vss to Vera as in the caseof the potential of the cell well. If the potential of the Row shieldline becomes Vera, each word line in the unselected memory cell blockssufficiently rises to the erase potential Vera or a potential close toVera by the capacitive coupling between the cell well and the word line,and erroneous data erase does not, therefore, occur.

Further, in the second memory cell block shown in FIG. 15, a word linedriver select signal line instead of the Row shield line is arranged onthe memory cell array. During the erase operation, the word line driverselect signal line turns into a floating state. Also, the potential ofthe bit line becomes Vera. Each word line in the unselected memory cellblocks sufficiently rises to the erase potential Vera or a potentialclose to Vera by the capacitive coupling between the cell well and theword line, and erroneous data erase does not, therefore, occur.

If the potential of either the row shield line or the block select lineis, for example, Vss or Vdd, a large capacity is generated between theword line and the row shield line or block select line in the memorycells under the row shield line or the block select line. As a result,it becomes difficult to boost the word line to thereby cause erroneousdata erase.

After the erase potential (erase pulse) Vera is applied to the cellwell, an erase verify operation is conducted to verify whether or notdata has been erased sufficiently. The erase verify operation consistsof an erase verify read operation for reading memory cell data afterapplying the erase pulse to the cell well and “Erase completiondetection” for detecting whether or not a column which data has not beenerased sufficiently exists.

In the memory cell circuit in this embodiment (e.g., see FIG. 9), onedata circuit is common to the two bit lines BLe and BLo. Due to this,after conducting the erase verify read operation to the memory cellsconnected to the even-numbered bit line BLe, “Erase completiondetection” is conducted to detect whether or not all the data of all thememory cells connected to the even-numbered bit line BLe have beenerased.

Then, after conducting the erase verify read operation to memory cellsconnected to, for example, the odd-numbered bit line BLo, “Erasecompletion detection” is conducted to detect whether or not the data ofall memory cells connected to the odd-numbered bit line BLo have beenerased.

If it is confirmed that the data of all the selected memory cells havebeen erased sufficiently, the erase operation is completed. If there isa memory cell which data has been erased deficiently, an erase operation(supply of an erase pulse) is executed again.

The erase operation will be described in detail with reference to theoperation timing view hereinafter.

3.-1. Supply of Erase Pulse

FIG. 46 shows operation timing relating to the supply of an erase pulse.

<Odd-Numbered Memory Cell Block>

In an odd-numbered memory cell block, the word lines in this block andthe word line control circuit (row address decoder and word line driver)for controlling the potentials of select gate lines are arranged at oneside of the memory array as already described above. Description will begiven hereinafter while taking the first memory cell block as anexample.

If the first memory cell block is selected, the potential of the outputsignal RDECAD of the row address decoder RADD1 shown in FIG. 16 becomesVdd and the potential of the node TransferG1 in the word line driverRMAIN1 shown in FIG. 17 is set at Vdd. The potentials of the signallines CG1, CG2, . . . CG16 are set at the ground potential Vss by theswitching circuit (FIG. 8). Further, the potentials of the signal linesSGD and SGS are set at Vdd.

At this time, the potentials of the word lines WL1, WL2, . . . WL16 areset at the ground potential Vss and the potentials of the select gatelines SG1 and SG2 are set at Vdd−Vth (where Vth is the threshold voltageof the MOS transistor HNt1) and the select gate lines SG1 and SG2 turninto a floating state.

If the first memory cell block is not selected, the potential of theoutput signal RDECAD of the row address decoder RADD1 shown in FIG. 16becomes Vss and the potential of the node TransferG1 in the word linedriver RMAIN1 shown in FIG. 17 is set at Vss. As a result, each of theword lines WL1, WL2, . . . WL16 has the ground potential Vss and turnsinto a floating state.

Further, the MOS transistors HN7 and HN8 are turned on and the potentialof SGDS is Vdd. Due to this, each of the select gate lines SG1 and SG2has a potential of Vdd−Vth (where Vth is the threshold voltage of theMOS transistors HN7 and HN8) and turn into a floating state.

<Even-Numbered Memory Cell Block>

In an even-numbered memory cell block, the row address decoder in theword line control circuit for controlling the potentials of the wordlines and the select gate lines in this block, is arranged at one sideof the memory cell array and the word line driver is arranged at theother side of the memory cell array. Description will be givenhereinafter, while taking the second memory cell block as an example.

First, at period ECLK2, the potential of ROWPROG1 becomes Vss, that ofROWPROG1B becomes Vdd, and the clocked inverters CINV5 and CINV6 in theword line driver RMAIN2 shown in FIG. 19 turn into a non-operationstate. Then, at period ECLK3, the potential of ROWERASE1 becomes Vdd,that of ROWERASE1B becomes Vss and the clocked inverters CINV3 and CINV4in the row address decoder RADD2 shown in FIG. 18 turn into anon-operation state and an operation state, respectively.

If the second memory cell block is selected, the potential of RDECADS1becomes Vdd. Due to this, the potential of the output signal RDECADS ofthe row address decoder RADD2 shown in FIG. 18 becomes Vss. Further, ifthe second memory cell block is not selected, the potential of theoutput-signal RDECADS1 becomes Vss. Due to this, the potential of theoutput signal RDECADS of the row address decoder RADD2 shown in FIG. 18becomes Vdd.

Thereafter, at period ECLK4, when the potential of ROWERASE2 becomes Vddand that of ROWERASE2B becomes Vss, the clocked inverter CINV7 turnsinto an operation state.

As a result, if the second memory cell block is selected, the potentialof RDECADS2 becomes Vdd. Due to this, the potential of the nodeTransferG2 in the word line driver shown in FIG. 19 becomes Vdd. On theother hand, if the second memory cell block is not selected, thepotential of RDECADS2 becomes Vss. Due to this, the potential of thenode TransferG2 in the word line driver shown in FIG. 19 becomes Vss.

Then, at period ECLK5, when the potential of ROWERASE3 n becomes Vsswhile the second memory cell block is not selected (the potential ofRDECADS2 is Vss), the data is latched.

At period ECLK6, when the potential of ROWGATE becomes Vss while thesecond memory block is not selected (the potential of RDECADS is Vdd),the MOS transistors DHN6 and DHN9 (FIGS. 18 and 19) are cut off and theword line driver select signal line 22 (FIG. 15) turns into a floatingstate.

As can be seen from the above, whether the odd-numbered memory cellblock or the even-numbered memory cell block is selected, the potentialsof the word lines in the selected memory cell block are set at Vss andthe word lines and select gate lines in the unselected blocks turn intoa floating state at period ECLK6.

Further, in the even-numbered memory cell block, if the block is notselected, the word line driver select signal 22 (FIG. 15) has apotential Vdd and turns into a floating state.

Thereafter, at period ECLK7, the potential of the cell well CPWELL isset at Vera (e.g., about 20V). At this moment, in the selected block, ahigh electric field is applied between the word line (which potential isset at ground potential Vss) and the cell well, electrons in thefloating gate electrode of each memory cell are emitted to the cell welland data erase is executed.

Moreover, in the unselected block, at period ECLK7, when the potentialof cell well CPWELL is set at Vera (e.g., about 20V), the potential ofeach word line rises to Vera or a potential close to Vera by thecapacitive coupling between the word line and the cell well. At thismoment, the potential of the word line driver select signal 22 (FIG. 15)also rises by the capacitive coupling between the word line driverselect signal and the cell well.

Accordingly, in the unselected block, a high electric field is notapplied between the word line and the cell well, electrons in thefloating gate electrode of each cell are not, therefore, emitted to thecell well and data erase is not executed.

The reason for setting the potentials of BIASe and BIASo at Vdd atperiod ECLK8 is to decrease the surface leak current of the drains ofthe MOS transistors HN1 e and HN1 o (FIG. 9).

After period ERCV1, a recovery operation after data erase is conducted.

If the potential of the cell well CPWELL decreases from Vera to about10V, BLCRL is grounded to Vss and the charges of the bit lines BLe andBLo are discharged. If the potential Vera is about 10V, the potentialsof the bit lines BLe and BL0 decrease to about 12V by the capacitivecoupling between the bit lines BLe and BLo and the cell well CPWELL.

Accordingly, the MOS transistors HN1 e and HN1 o (FIG. 9) do not snapback.

If BLCRL is grounded to Vss and the charges of the bit lines BLe and BLoare discharged while the potential of the cell well CPWEL1 is about 20V,the MOS transistors HN1 e and HN1 o (FIG. 9) snap back and thesetransistors are disadvantageously broken.

3.-2. “Erase Verify Read”

FIG. 47 shows operation timing for Erase verify read.

In this embodiment, it is assumed that an erase verify read operation isconducted to memory cells connected to the even-numbered bit line BLeand that the odd-numbered bit line BLo is used as shield bit lines. Inthe Erase verify read operation, the potential of the shield bit lineBLo is set at Vdd.

First, at period RCLK1, the potential of CAPCRG is set at Vdd. At periodRCLK2, the potential of BLCLMP is set at Vclmp (e.g., about 2V). Atperiod RCLK5, when the potential of REG1 becomes Vdd, the potential ofthe selected bit line BLe is set at Vss (0V) (while the potential ofVREG is Vss and that of CAP1 ij is Vdd).

At period RCLK7, the potential of the selected word line (control gateelectrode) CGselect is set at Vcgev (e.g., 0V) and that of the selectgate line SGD is set at Vread (e.g., about 3.5V) (while the potential ofSGS is Vread).

The Erase verify read operation is usually conducted almostsimultaneously to the memory cells connected to the bit line BLe andconnected to all the word lines in the selected block. Due to this, thepotentials of all word lines WL1, WL2, . . . WL16 in the selected blockare set at Vcgev.

As a result, when the data of all the memory cells (memory cell in oneNAND cell unit) connected to one bit line BLe in the selected one blockhave been erased sufficiently, the level of the one bit line BLe becomes“H”. Also, the data of at least one memory cell has been eraseddeficiently among the memory cells connected to one bit line in theselected one block, the level of the one bit line BLe becomes “L”.

In the Erase verify read operation, the potentials of unselected bitlines BLo are set at Vdd so as to reduce coupling noise generatedbetween the bit lines.

After the potentials of the respective bit lines BLe have beendetermined, the potentials of the bit lines BLe are sensed as in thecase of an ordinary read operation.

If the data of all memory cells connected to one bit line BLe in theselected one block have been erased sufficiently, the level of the sensenode DTNij (the output node Naij of the latch circuit LATCH1) in thedata circuit to which the one bit line BLe is connected, becomes “H”.

Further, if the data of at least one memory cell has been eraseddeficiently among the memory cells connected to one bit line BLe in theselected one block, the level of the sense node DTNij (the output nodeNaij of the latch circuit LATCH1) in the data circuit to which the onebit line BLe is connected, becomes “L”.

3.-3. “Erase Completion Detection”

FIG. 48 shows operation timing relating to Erase completion detection.

After the Erase verify read operation, “Erase completion detection” fordetecting whether or not erase has been completed in all columns. InFIG. 12, when the levels of the output nodes Naij of the latch circuitsLATCH1 in all data circuits are “H”, the FLAG node maintains “H”. InFIG. 12, when the level of the output node Naij of the latch circuitLATCH1 in at least one data circuit is “L”, the level of the FLAG nodebecomes “L”.

Since the FLAG node is connected to all columns, the data of at last onememory cell among the memory cells in the selected one block has beenerased deficiently, the level of the FLAG node becomes “L” and an erasepulse is supplied again. If the data of all memory cells in the selectedone block have been erased sufficiently, the level of the FLAG nodebecomes “H” and the erase operation is completed.

Since “Erase completion detection” is almost the same as “Programcompletion detection” in the above-described “even page data programoperation”, the detailed description of the operation is not givenherein.

4. Burn-in Mode

In a burn-in mode for testing the reliability of MOS transistors (MOStransistors other than the memory cells) constituting the peripheralcircuits, the value of the power supply potential Vdd is set at a highervalue (e.g., about 3.5V) than a value (e.g., about 2.3V) used during anordinary operation.

In this case, the power supply potential Vdd (e.g., about 3.5V) isapplied to the node CAP2 ij in the data circuit shown in FIG. 9.Accordingly, in the burn-in mode, if the value of the power supplypotential Vdd is set too high, the potential of node CAP2 ij becomesexcessively high by capacitive coupling when the potential of BOOTchanges from Vss to Vdd and the gate (MOS capacitor) of the MOStransistor DLN1 in the data circuit shown in FIG. 9 is disadvantageouslybroken.

To overcome such disadvantage, the potential of BOOT in the data circuitshown in FIG. 9 can be fixed to Vdd in the burn-in mode. In that case,since the potential of the node CAP2 ij is always not higher than Vdd, ahigh voltage is not applied excessively to the gate oxide film(capacitor insulating film) of the MOS transistor DLN1.

Therefore, the gate of the MOS transistor DLN1 can be prevented frombeing broken.

5. DRAM Burn-in Mode

As described above, in principle, the potential Vdd cannot be applied tothe node CAP2 ij (DRAM cell) in the data circuit shown in FIG. 9. Then,a burn-in mode is executed to the DRAM cell at operation timing shown inFIG. 49 as follows.

FIG. 49 shows a mode for conducting a Burn-in test to the DRAM cell byapplying a high potential different from Vdd to the node CAP2 ij (DRAMcell).

First, Vext (power supply potential supplied externally of the chip) isapplied to VREG. Also, the MOS transistor TN4 (FIG. 9) is turned onsince the potential of CAPCRG is VSG.

The potential of the node CAP2 ij is, therefore, fixed to Vext. It isnoted that Vext is set at such a predetermined value as not to destroythe MOS capacitor DLN1.

In this embodiment, the potential of DTG1 becomes Vsg thereafter and thepotential Vdd is supplied from the node Naij to the node CAP1 ij (DRAMcell).

As can be seen, in this embodiment, a reliability test to the DRAM cellin the data circuit shown in FIG. 9 is conducted by “DRAM Burn-in mode”shown in FIG. 49 and a reliability test to the peripheral circuit otherthan the DRAM cell is conducted by an ordinary “Burn-in mode”.

Further, “DRAM Burn-in mode”, i.e., the reliability test to the DRAMcell can be conducted simultaneously with the reliability test to theperipheral circuits other than the DRAM cell.

6. “Refresh” . . . Fifth Feature

In this embodiment, at least one storage circuit among a plurality ofstorage circuits used to temporarily store multi-level data (e.g.,four-level data) is constituted by a DRAM cell (capacitor). If there isa leakage problem, it is necessary to regularly conduct a refreshoperation to the DRAM cell.

For example, in the odd page data program operation, the even page dataprogram data (data read from the memory cell) is latched by the nodeCAP1 ij(DRAM cell). Here, there is a problem with data holdingcapability of the node CAP1 ij due to the leakage of charges of the nodeCAP1 ij, the data of the node CAP1 ij may be refreshed regularly.

FIG. 50 shows operation timing in case of refreshing the node CAP1 ijdata during the program operation.

It is noted that PRCV1 corresponds to PRCV1 shown in FIG. 29 (the supplyof program pulse).

At period PRCV1, as can be understood from FIG. 29, the charges of theword line are discharged. At period RFCLK1 (PRCV1), the level of BLCbecomes “L” and the data circuit is disconnected from the bit line Atthis moment, the odd page program data is held by the bit line.

At period RFCLK1, the potentials of SEN and LAT becomes Vss and those ofSENB and LATB become Vdd. As a result, the clocked inverters CINV1 andCINV2 turn into a non-operation state and the nodes Naij and Nbij turninto a floating state.

Then, at period RFCLK2, the level of EQPB becomes “H” and the potentialof the node Naij and that of the node Nbij are equalized. The MOScapacitor DLN3 shown in FIG. 9 is provided to make the capacity of thenode Naij and that of the node Nbij almost equal to each other.

At period RFCLK4, the potential of DTG1 becomes Vsg and the data (evenpage data) of the node CAP1 ij is transferred to the node Naij.

At period RFCLK5, when the level of SEN becomes “H” and that of SENBbecomes “L”, the data of the node CAP1 ij is sensed by the clockedinverter CINV1. At period RFCLK6, when the level of LAT becomes “H” andthat of LATB becomes “L”, the data (even page data) of the node CAP1 ijis latched by the latch circuit LATCH1.

At this point, the data of the node CAP1 ij is refreshed. At periodRFCLK7, when the potential of DTG1 becomes Vss, the refreshed even pagedata is stored again in the node CAP1 ij.

Thereafter, the odd page data held by the bit line is returned to thelatch circuit LATCH1.

First, at period RFCLK8, the potentials of SEN and LAT become Vss andthose of SENB and LATB become Vdd. As a result, the clocked invertersCINV1 and CINV2 shown in FIG. 9 turn into a non-operation state and thenodes Naij and Nbij turn into a floating state.

At period RFCLK9, when the potential of BLC becomes Vsg, the odd pagedata held by the bit line is transferred to the node Naij.

At period RFCLK10, when the level of SEN becomes “H” and that of SENBbecomes “L”, the odd page data is sensed by the clocked inverter CINV1.At period RFCLK11, when the level of LAT becomes “H” and that of LATBbecomes “L”, the odd page data is latched by the latch circuit LATCH1.

In the refresh operation in this embodiment, while the even page dataheld by the node CAP1 ij is being refreshed, the odd page data is heldby the bit line.

Accordingly, after the odd page data held by the bit line is returned tothe latch circuit LATCH1, the discharge of the bit line (the dischargeof the bit line after programming) is carried out. Namely, period RFCLKshown in FIG. 50 should be always before period PRCV3 shown in FIG. 29(the supply of a program pulse).

[Modification of Data Circuit: 1] . . . Sixth and Seventh Features

FIG. 51 shows a modification of the data circuit.

Compared with the data circuit shown in FIG. 9, the data circuit in thismodification is characterized by providing a write cache WCS21.

The write cache WCS1 is constituted by a DRAM cell.

Now, advantages obtained by using the write cache will be described.

In the program operation conducted over a plurality of pages (e.g.,after programming the memory cells connected to the word line WL1,memory cells connected to the word line WL2 are programmed and thenmemory cells connected to the word line WL3 are programmed), the inputof program data and program (the supply of a program pulse) areconventionally conducted alternately and serially as shown in FIG. 52.

In case of providing a write cache in the data circuit, by contrast, theinput of program data and the program (the supply of a program pulse)can be conducted in parallel as shown in FIG. 53.

For example, in FIG. 51, the program data on the memory cells (“Page1”)connected to the word line WL1 is inputted by the latch circuit LATCH1and “Page1” is programmed. Further, program data on the memory cells(“Page2”) connected to the word line WL2 is inputted into the writecache WCS1 during the program to “Page1”.

After the completion of programming “Page1”, the “Page2” program dataheld by the write cache WCS1 is transferred to the latch circuit LATCH1and “Page2” is programmed. Also, program data on the memory cells(“Page3”) connected to the word line WL3 is inputted into the writecache WCS1 while programming “Page2”.

In this way, according to the data circuit provided with the write cacheWCS1, program data on a page to be programmed next is loaded to thewrite cache WCS1 while programming a present page (supplying a programpulse). This can dispense with time for loading-program data afterpage2. As a result, the program operation is accelerated.

Now, with regard to the write cache WCS1, operation timing during theprogram operation will be described in detail.

{circle around (1)} Data Input into Write Cache

FIG. 54 shows operation timing for inputting data into the write cache.

Before inputting the program data, the potential of PR is kept Vsg. As aresult, the potential of the node CAP3 ij (DRAM cell) is Vdd. When acommand of “input data into write cache WCS1” is inputted into the chip,the potential of PR changes from Vsg to Vss, the potential of the nodeCAP3 ij becomes Vdd and the node CAP3 ij turns into a floating state atperiod WCCLK1.

Then, at period WCCLK2, when the potential of CSL2 i becomes Vdd, datais inputted into the write cache WCS1 from the input/output line IOj. Incase of data “0”, the potential of IOj is Vss and that of the node CAP3ij, therefore, becomes Vss (0V). In case of data “1”, the potential ofIOj is Vdd and that of the node CAP3 ij is, therefore, kept Vdd.

While data is being inputted into the write cache WCS1, the potential ofTG is Vs. Due to this, the write cache WCS1 and the latch circuit LATCH1are electrically disconnected from each other. Therefore, even whiledata is being inputted into the write cache WCS1, program and verifyread operations and the like can be executed based on the program datalatched by the latch circuit LATCH1.

If program data is not inputted into the write cache WCS1, the potentialof the node CAP3 ij is Vdd, i.e., “1”-programming data is held by thenode CAP3 ij. As a result, columns which data are not inputted into thewrite cache WCS1 are not programmed.

{circle around (2)} Data Transfer from Write Cache to Latch. Circuit

When the operation for writing the data latched by the latch circuitLATCH1 into the memory cells, the data held by the write cache WCS1 istransferred to the latch circuit LATCH1 and a program operation isexecuted based on the data.

FIG. 55 shows operation timing for transferring data from the writecache WCS1 to the latch circuit LATCH1.

First, at period WLCK1, the potentials of SEN and LAT become Vss andthose of SENB and LATB become Vdd. As a result, the latch circuit LATCH1turns into a non-operation state. Then, at period WLCLK2, the potentialof EQPB becomes Vdd and the potential of the node Naij and that of thenode Nbij are equalized.

Thereafter, at period WLCLK4, when the potential of TG becomes Vsg, thedata in the write cache WCS1 is transferred to the node Naij. At periodWLCLK5, when the potential of SEN becomes Vdd and that of SENB becomesVss, the data of the node Naij is sensed by the clocked inverter CINV1.At period WLCLK6, when the potential of LAT becomes Vdd and that of LATBbecomes Vss, the data of the node Naij is latched by the latch circuitLATCH1.

In this way, the data held by the node CAP3 ij of the write cache WCS1is transferred to the latch circuit LATCH1. After the data in the writecache WCS1 is transferred to the latch circuit LATCH1, the potential ofTG becomes Vss at period WLCLK7.

Thereafter, the potential of PR is set at Vsg, that of CAP3 ij is set atVdd and the next program data is inputted into the write cache WCS1(FIG. 54).

{circle around (3)} Refresh of Data in Write Cache

If the data holding capability of the node CAP3 ij by the leakage of thecharges of the node (DRAM cell) CAP3 ij in the write cache WCS1 causes aproblem, the data of the node CAP3 ij is regularly refreshed.

FIG. 56 shows operation timing for refreshing the data of the node CAP3ij during the program operation.

It is noted that PRCV1 corresponds to PRCV1 shown in FIG. 29 (the supplyof a program pulse).

First, at period PRCV1, as can be understood from FIG. 29, the wordlines are discharged. At period WRFCLK1 (PRCV1), the level of BLCbecomes “L” and the data circuit is electrically disconnected from thebit lines. While refreshing the write cache WCS1, the program data inthe latch circuit LATCH1 are made to wait in the bit lines.

Namely, at period WRFCLK1, the potentials of SEN and LAT become Vss andthose of SENB and LATB become Vdd. As a result, the clocked invertersCINV1 and CINV2 shown in FIG. 51 turn into a non-operation state and thenodes Naij and Nbij turn into a floating state.

Thereafter, at period WRFCLK2, the level of EQPB becomes “H” and thepotential of the node Naij and that of the node Nbij are equalized. Itis noted that the MOS capacitor DLN3 shown in FIG. 51 is provided tomake the capacity of the node Naij and that of the node Nbij almostequal to each other.

At period WRFCLK4, the potential of TG becomes Vsg and the data of thenode CAP3 ij of the write cache WCS1 is outputted to the node Naij. Atperiod WRFCLK5, when the level of SEN becomes “H” and that of SENBbecomes “L” the data in the write cache WCS1 is sensed by the clockedinverter CINV1. At period WRFCLK6, when the level of LAT becomes “H” andthat of LATB becomes “L”, the data in the write cache WCS1 is latched bythe latch circuit LATCH1.

By this point, the data (potential of the node CAP3 ij) in the writecache WCS1 has been refreshed. Then, at period WRFCLK7, when thepotential of TG becomes Vss, the data in the write cache WCS1 thusrefreshed is held again by the node CAP3 ij.

Thereafter, an operation for returning the program data which are madeto wait in the bit lines, to the latch circuit LATCH1 is executed.

First, at period WRFCLK8, the potentials of SEN and LAT become Vss andthose of SENB and LATB become Vdd. As a result, the clocked invertersCINV1 and CINV2 shown in FIG. 51 turn into a non-operation state and thenodes Naij and Nbij turn into a floating state.

At period WRFCLK9, when the potential of BLC becomes Vsg, the bit linesare electrically disconnected from the data circuit and the program dataheld by the bit lines is transferred to the node Naij. At periodWRFCLK10, when the level of SEN becomes “H” and that of SENB becomes“L”, the program data is sensed by the clocked inverter CINV1. Further,at period WRFCLK11, when the level of LAT becomes “H” and that of LATBbecomes “L”, the program data is latched by the latch circuit LATCH1.

In this way, in the refresh operation conducted to the data in the writecache WCS1, while the data held by the node CAP3 ij is being refreshed,the program data latched by the latch circuit LATCH1 is held by the bitlines.

Accordingly, after refreshing the data in the write cache WCS1 andreturning the program data held by the bit lines to the latch circuitLATCH1, the discharge of the bit lines (the discharge of the bit linesafter the program operation) is executed. Namely, period WRFCLK12 shouldbe always before PRCV3 in FIG. 29 (the supply of a program pulse).

[Modification of Data Circuit: 2] . . . Sixth Feature FIG. 57 shows amodification of the data circuit.

Compared with the data circuit shown in FIG. 51, the data circuit inthis modification is characterized in that the write cache WCS2 isconstituted by an SRAM cell.

In the modification of FIG. 51, the write cache is constituted by a DRAMcell. In this modification, the write cache is constituted by an SRAMcell. In either case, the input of program data can be made in parallelwith the program operation (the supply of a program pulse). Thus, theadvantage of accelerating program speed can be obtained.

Now, with regard to the write cache WCS2, operation timing during theprogram operation will be described in detail.

{circle around (1)} Data Input into Write Cache

FIG. 58 shows operation timing for inputting data into the write cache.

Before inputting program data, the potential of PR3 is kept Vdd. When acommand of “input data into write cache WCS2” is inputted into the chip,the potential of PR3 changes from Vdd to Vss, that of the node Ncijbecomes Vdd and that of the node Ndij is set at Vss.

Then, at period WACLK2, when the potential of CSL3 i becomes Vdd, datais inputted into the write cache WCS2 from the input/output line IOj. Incase of data “0”, since the potential of IOj is Vss, that of nIOj isVdd, the potential of the node Ncij of the SRAM cell becomes Vss andthat of the node Ndij becomes Vdd. In case of data “1”, since thepotential of IOj is Vdd and that of the nIOj is Vss, the potential ofthe node Ncij of the SRAM cell becomes Vdd and that o the node Ndijbecomes Vss.

While data is being inputted into the write cache WCS2, the potential ofTG3 is Vss. Due to this, the write cache WCS2 and the latch circuitLATCH1 are electrically disconnected from each other. Therefore, evenwhile data is being inputted into the write cache WCS2, the program andverify read operations for the data can be executed based on the programdata held by the latch circuit LATCH1.

In FIG. 57, if data is not inputted into the write cache WCS2, thepotential of the node Ncij becomes Vdd and that of the node Ndij becomesVss. Namely, the write cache WCS2 holds “1”-programming data. As aresult, columns which data are not inputted into the write cache WCS2are not programmed.

{circle around (2)} Data Transfer from Write Cache to Latch Circuit

When the program operation for the data latched by the latch circuitLATCH1 has been completed, the data held by the write cache WCS2 istransferred to the latch circuit LATCH1 and a program operation iscarried out.

FIG. 59 shows operation timing for transferring data from the writecache WCS2 to the latch circuit LATCH1.

First, at period WBCK1, the potentials of SEN and LAT become Vss andthose of SENB and LATB become Vdd. As a result, the latch circuit LATCH1turns into a non-operation state. Then, at period WBCLK2, when thepotential of TG3 becomes Vsg, the data in the write cache WSC2 (data ofthe node Ncij) is transferred to the node Naij. At period WBCLK3, whenthe potential of SEN becomes Vdd and that of SENB becomes Vss, the dataof the node Naij is sensed by the clocked inverter CINV1. At periodWLCLK4, when the potential of LAT becomes Vdd and that of LATB becomesVss, the data of the node Naij is latched by the latch circuit LATCH1.

In this way, the data held by the node Ncij of the write cache WCS2 istransferred to the latch circuit LATCH1. After the data in the writecache WCS2 is transferred to the latch circuit LATCH1, the potential ofTG3 becomes Vss and the latch circuit LATCH1 is electricallydisconnected from the write cache WCS2 at period WLCLK5.

Thereafter, the potential of PR3 is set at Vss and that of Ncij is setat Vdd. Then, the next program data is inputted into the write cacheWCS2 (FIG. 58).

In this example, the write cache WCS2 is constituted by a SRAM.Therefore, “data refresh in the write cache” is not necessary.

[Program Speed]

1. Overview

In the conventional Flash memory, one data circuit is connected per bitline to which memory cells to be programmed are connected. The datacircuit is provided with a storage circuit (e.g., a latch circuit) fortemporarily storing program data on a selected memory cell.

In case of an ordinary two-level Flash memory, one storage circuit forholding one-bit program data is provided in one data circuit. In case ofa multi-level memory, a plurality of storage circuits for storingprogram data of not lower than three levels are provided.

In an actual program operation, it is determined whether or not aprogram operation to a selected memory cell is executed (e.g., whetheror not electrons are to be injected into the floating gate electrode)based on the program data stored by the data circuit.

In this way, in the conventional Flash memory, one data circuit fortemporarily storing program data is provided per bit line to whichmemory cells to be programmed are connected. Namely, if 4,000 datacircuits exist in a chip, 4,000 memories can be programmed almostsimultaneously.

Accordingly, if the number of data circuits increases, program speed canbe accelerated. Providing that 8,000 data circuits are provided in achip, 8,000 memory cells can be programmed almost simultaneously. Inthat case, program speed can be doubled compared with a case ofproviding 4,000 data circuits in a chip.

However, the increase of the number of data circuits in a chip means theincrease of a chip area. Further, if the chip area increases, cost perbit is disadvantageously pushed up.

The invention to be described hereinafter is intended to solve theabove-stated disadvantage. The invention is characterized in that twomemory cells can be programmed almost simultaneously using one datacircuit.

Quite naturally, as in the case of the conventional memory, a storagecircuit (e.g., a latch circuit) capable of temporarily storing onlyprogram data (two-level or multi-level data) on one memory cell isprovided. In case of a two-level memory, for example, only one storagecircuit capable of temporarily storing one-bit data is provided in onedata circuit.

The present invention, therefore, can accelerate program speed almosttwice as fast as the conventional program speed by programming twomemory cells almost simultaneously using one data circuit withoutincreasing a chip area.

2. Gist of the Present Invention

First, the gist of the present invention will be described (FIGS. 60A to60D).

As already stated above, the present invention is characterized in thattwo memory cells are programmed almost simultaneously using one datacircuit.

It is noted that only a storage circuit for temporarily storing programdata on one memory cell is provided in the data circuit as in the caseof the conventional memory (which prevents a chip area from increasing).That is, the present invention proposes a technique for doubling programspeed without increasing a chip area by contriving a program operation(program control by a control circuit).

The present invention will be described hereinafter, while taking atwo-level NAND type Flash memory as an example.

In the present invention, it is assumed that at least two bit lines BLAand BLB are connected to one data circuit. Further, these two bit linesBLA and BLB are arranged in different banks. That is to say, it isassumed that the control gate line (word line) of memory cells connectedto the bit line BLA always differs from the control gate line (wordline) of memory cells connected to the bit line BLB. In this case, thetwo bit lines BLA and BLB are arranged in an open state relative to eachother about, for example, the data circuit, without arranging them toadjacently face each other.

Therefore, the present invention precludes a case where two bit linesare connected to one data circuit and arranged, for example, toadjacently face each other. It is noted, however, that the presentinvention can be combined with such a shield bit read method (which willbe described in detail).

Description will now be given to the program operation (only the gistthereof).

A concrete program operation will be described below.

It is assumed that selected memory cells are a memory cell CellAconnected to the bit line BLA and a memory cell CellB connected to thebit line BLB. A program operation is executed almost simultaneously tothe two memory cells CellA and CellB using one data circuit (which canhold only program data on one memory cell).

First, program data on the memory cell CellA is held by the bit line BLAfrom externally of the chip by way of the data circuit. Likewise,program data on the memory cell CellB is held by the bit line BLB fromexternally of the chip by way of the data circuit.

As shown in FIGS. 60A and 60B, if executing the program operation to thememory cell CellA, the level of TGA is set at “L” and that of TGB is setat “H”.

Namely, since a transfer gate TrNA is turned off, the bit line BLA is ina floating state and the bit line BLA holds program data on the memorycell CellA. At this moment, a program pulse is supplied to the controlgate line (word line) of the memory cell CellA. Due to this, a programoperation is executed to the memory cell CellA according to the programdata of the bit line BLA.

In case of “0”-programming (program select), for example, the potentialof the bit line BLA is 0V (“Low”, i.e., program data “0”) and thepotential of the channel of the memory cell CellA becomes 0V, as well.Accordingly, a high voltage is applied to the tunnel oxide film of thememory cell CellA and “0”-programming (the injection of electrons intothe floating gate electrode) is executed to the memory cell CellA.

In case of “1”-programming (write inhibit), the level of the bit lineBLA is Vdd (“High”, i.e., program data “1”) and the potential of thechannel of the memory cell CellA becomes, for example, Vdd−Vth (whereVth is the threshold voltage of a select transistor) and the memory cellCellA is disconnected from the bit line BLA (the select transistor iscut off).

Therefore, even if a program pulse is supplied to the control gate line(word line), a channel potential rises by the capacitive couplingbetween the control gate line and the channel. As a result, a highvoltage is not applied to the tunnel oxide film of the memory cell CellAand “1”-programming (maintaining an erase state) is executed to thememory cell CellA.

While a program pulse is supplied to the memory cell CellA, the programdata is being held by the bit line BLA which is in a floating state. Atthis time, the program data on the bit line BLA has no change and thedata is stably held by the bit line BLA.

The reason is as follows. Since the bit line BLA has sufficient highcapacity, the potential of the bit line BLA which is in a floating statedue to the capacitive coupling, little changes even if a program pulseis supplied to the control gate line during “0”-programming. Inaddition, since a tunnel current flowing from the floating gateelectrode of the memory cell CellA to the bit line BLA is quite low, thetunnel current hardly influences the potential change of the bit lineBLA.

Meanwhile, while a program pulse is being supplied to the memory cellCellA, a transfer gate TrNB is kept to be turned on and the bit line BLBis electrically connected to the data circuit 2-i.

If no program operation, for example, is conducted to the memory cellCellB, program data (“0” or “1”) held by the bit line BLB may berefreshed while supplying a program pulse to the memory cell CellA. Thisis because the bit line BLB turns into a floating state during theprogram operation and the data held by the bit line BLB may possiblychange by leakage (leakage of charges).

The refresh operation is conducted by transferring the program data heldby the bit line BLB to the storage circuit (e.g., latch circuit) in thedata circuit 2-i, sensing and latching the program data by the storagecircuit and returning the program data again to the bit line BLB.

On the other hand, after a program pulse is supplied to the memory cellCellB, a operation for verifying the state of the memory cell CellB(whether or not the program operation has been successfully conducted toCellB), i.e., a program verify operation is carried out while applying aprogram pulse to the memory cell CellA.

First, the program data on the memory cell CellB held by the bit lineBLB is transferred to and held by the storage circuit in the datacircuit 2-i (FIG. 60A). Then, the data of the memory cell CellB is read(verify read) and, for example, the program data held by the storagecircuit in the data circuit 2-i is compared with the read data of thememory cell CellB.

If the both data are coincident with each other, it is determined asProgram OK and electrons are not injected into the memory cell CellBthereafter. If the both data are not coincident, it is determined asProgram NG and the program operation is continuously conducted to thememory cell CellB.

That is to say, the reprogram data held by the storage circuit in thedata circuit 2-i is returned to the bit line BLB and then a programpulse is supplied to the memory cell CellB.

Further, as shown in FIGS. 60C and 60D, after a program pulse issupplied to the memory cell CellA, the level of TGA is set at “H” andthat of TGB is set at “L”.

Namely, since the transfer gate TrNB is turned off, the bit line BLB isin a floating state and the bit line BLB holds the program data on thememory cell CellB. At this time, since a program pulse is supplied tothe control gate line (word line) of the memory cell CellB, a programoperation is executed to the memory cell CellB according to the programdata on the memory cell CellB.

In case of “0”-programming (program select), for example, the potentialof the bit line BLB is 0V (“Low”, i.e., program data “0”) and thepotential of the memory cell CellB becomes 0V, as well. Accordingly, ahigh voltage is applied to the tunnel oxide film of the memory cellCellB and “0”-programming (the injection of electrons into the floatinggate-electrode) is executed to the memory cell CellB.

In case of “1”-programming (write inhibit), the potential of the bitline BLB is Vdd (“High”, i.e., program data “1”), the potential of thechannel of the memory cell CellB becomes Vdd−Vth (where Vth is thethreshold voltage of the select transistor) and the memory cell CellB isdisconnected from the bit line BLB (the select transistor is cuts off).

Accordingly, even if a program pulse is supplied to the control gateline (word line), a channel potential rises by the capacitive couplingbetween the control gate line and the channel. As a result, a highvoltage is not applied to the tunnel oxide film of the memory cell CellBand “1”-programming (maintaining an erase state) is executed to thememory cell CellB.

While a program pulse is being supplied to the memory cell CellB, theprogram data is held by the bit line BLB which is in a floating state.At this time, for the same reason as that described above, the programdata of the bit line BLB has no change and the program data is stablyheld by the bit line BLB.

Meanwhile, in FIGS. 60C and 60D, the transfer gate TrNA is kept to beturned on, the bit line BLA is electrically connected to the datacircuit 2-i and a verify read operation is conducted to the memory cellCellA.

First, the program data on the memory cell CellA held by the bit lineBLA is transferred to and held by the storage circuit in the datacircuit 2-9 (FIG. 60C). Then, the data of the memory cell CellA is read(verify read) and, for example, the program data held by the storagecircuit in the data circuit 2-i is compared with the read data of thememory cell CellA.

If the both data are coincident with each other, no electrons areinjected into the memory cell CellA thereafter. If the both data are notcoincident, the program operation is continuously conducted to thememory cell CellA.

That is to say, the reprogram data held by the storage circuit in thedata circuit 2-i is returned to the bit line BLA and then a programpulse is supplied to the memory cell CellA.

The operations shown in FIGS. 60A to 60D are repeatedly carried outuntil the memory cells CellA and CellB have been precisely programmed.

In this way, according to the present invention, one data circuitcorresponding to two selected memory cells (two bit lines) is provided.If so, while one of the memory cells is being programmed, program datais held by the bit line connected to the one memory cell and the bitline is electrically disconnected from the data circuit. At this moment,the bit line to which the other memory cell is connected is electricallyconnected to the data circuit and a verify operation is executed to theother memory cell.

With the above-stated constitution and control method, two selectedmemory cells can be programmed almost simultaneously using one datacircuit capable of temporarily holding only the program data on onememory cell. Thus, program speed can be accelerated (almost twice asfast as the conventional speed) without increasing a chip area.

It should be noted that the above description has been given to the gistof the present invention. Accordingly, using a similar technique, aprogram operation can be executed almost simultaneously to, for example,two or more selected memory cells using one data circuit.

3. Concrete Example 1

The concrete examples of the present invention will be describedhereinafter.

It is noted that description will be given, while taking a two-levelNAND type Flash memory as an example as in the case of the descriptionof the gist of the invention.

3.-1. Chip Layout

FIG. 61 is a schematic diagram of the chip layout of a two-level NANDtype flash memory according to the present invention.

The layout is characterized in that a memory cell array consists of anUpper bank and a Lower bank and that data circuits are arranged betweenthe Upper and Lower banks.

Namely, in this example, data circuits are common to the memory cells inthe Upper bank and those in the Lower bank. In that case, it is possibleto program one memory cell in the Upper bank and one memory cell in theLower bank almost simultaneously using one data circuit. Due to this,compared with the conventional memory (wherein one memory cell isprogrammed using one data circuit), program speed can be almost doubled.

The Upper bank consists of four banks, i.e., Bank1U, Bank2U, Bank3U andBank4U. The Lower bank consists of four banks, i.e., Bank1L, Bank2L,Bank3L and Bank4L, accordingly. The bit line BLA extends from the datacircuit toward the Upper bank and the bit line BLB extends from the datacircuit toward the Lower bank.

In this example, by one program operation (an operation from data inputto completion of program; the supply of a program pulse is normallyconducted a plurality of times), data program for eight pages, Page1U,Page2U, Page3U, Page4U, Page1L, Page2L, Page3L and Page4L (program toone page for one bank) can be carried out.

With the conventional program method, it is impossible to program amemory cells in the Upper bank and that in the Lower bank almostsimultaneously. For that reason, with the conventional method, only dataprogram for four pages can be carried out by one program operation.Namely, the present invention can make program speed almost twice asfast as the conventional program speed.

3.-2. Data Circuit

FIG. 62 shows one data circuit as well as bit lines and memory cellsconnected to the data circuit with regard to the chip layout shown inFIG. 61.

The data circuit 2-i includes a latch circuit LATCH1, an N channel MOStransistor TN31, verification P channel MOS transistors TP31 and TP32,precharge N channel MOS transistors TN32A, TN32B, TN32C and TN32D, andtransfer gates TrNA, TrNB, TrNC and TrND.

The latch circuit LATCH1 is employed to, for example, temporarily storeprogram/read data for program/read operations.

In this example, four bit lines BLA, BLB, BLC and BLD are connected toone data circuit 2-i. The two bit lines BLA and BLC are arranged in theUpper bank. The bit lines BLA and BLC are arranged to face each otherand to be adjacent each other. Also, the two bit lines BLB and BLD arearranged in the Lower bank. The bit lines BLB and BLD are arranged toface each other and to be adjacent each other.

During the program operation, one bit line is selected out of the twobit lines BLA and BLC in the Upper bank and one bit line is selected outof the two bit lines BLC and BLD in the Lower bank. Namely, using onedata circuit 2-i, two memory cells (one memory cell in the Upper bankand one memory cell in the Lower bank) are programmed almostsimultaneously.

The reason for connecting two bit lines in one bank to one data circuit2-i as shown in this example is intended to fix the potential of oneline out of the two bit lines to Vss or Vdd during the program/readoperations and to thereby prevent capacitive coupling noise between thebit lines during the program/read operations from occurring.

For example, during the program operation, the potential of oneunselected bit line out of the two bit lines BLA and BLC in the Upperbank is set at an internal power supply potential Vdd. By setting thepotential of the unselected bit line at Vdd (turning the unselected bitline in a write inhibit state), it is possible to eliminate capacitivecoupling noise between the bit lines during the program operation.Besides, erroneous program (“0”-programming) to the memory cellconnected to the unselected bit line can be prevented.

For the same reason, the potential of one, unselected bit line out ofthe two bit lines BLB and BLD in the Lower bank is set at the internalpower supply potential Vdd.

Further, as in this example, if two bit lines in one bank are connectedto one data circuit 2-i, a so-called shield bit line read method can beadopted during the read operation, thereby making it possible toeliminate capacitive coupling noise between the bit lines during theread operation. Namely, by using one bit line as a data read bit lineand the other bit line as a shield bit line (Vss), it is possible toaccelerate read speed and to prevent erroneous data read.

As can be seen from the above, in this example, if two memory cellsCellA and CellB are programmed using one data circuit 2-i, thepotentials of the two bit lines BLC and BLD are always set at a fixedpotential (Vdd or Vss). In addition, if two memory cells CellC and CellDare programmed using the data circuit 2-i, the potentials of the two bitlines BLA and BLB are always set at a fixed potential (Vdd or Vss).

Accordingly, during the program/read operations, it is possible toexecute the program/read operations without generating capacitivecoupling noise between the bit lines.

3.-3. Program Operation

FIG. 63 shows the detail of the program operation to the two memorycells CellA and CellB with regard to the memories shown in FIGS. 61 and62.

(1) Step1

First, Data load for loading data on the memory cell CellA in the Upperbank is conducted, i.e., program data on the memory cell CellA isinputted from externally of the chip into the data circuit 2-i in thechip.

Actually, data on four pages, i.e., Page1U, Page2U, Page3U and Page4Ufor the four banks, i.e., Bank1U, Bank2U, Bank3U and Bank4U, areinputted into a plurality of data circuits provided to correspond to thefour-page data, respectively.

Also, when the level of TGA becomes “H” and the transfer gate TrNA isturned on, the program data on the memory cell CellA is transferred fromthe data circuit 2-i to the bit line BLA in the Upper bank.

If the program data is, for example, “0” (“0”-programming or programselect), the potential of the bit line BLA becomes Vss (0V) and if theprogram data is “1” (“1”-programming or write inhibit), the potential ofthe bit line BLA becomes the internal power supply potential Vdd (e.g.,about 2.3V).

(2) Step2

First, the level of TGA becomes “L” and the transfer gate TrNA is turnedoff. As a result, the bit line BLA is electrically disconnected from thedata circuit 2-i and the program data on the memory cell CellA isenclosed (held) by the bit line BLA.

Thereafter, data load for the memory cell CellB in the Lower bank isconducted, i.e., the program data on the memory cell CellB is inputtedfrom externally of the chip into the data circuit 2-i in the chip.

Actually, data on four pages, i.e., Page1L, Page2L, Page3L and Page4Lfor the four banks, i.e., Bank1L, Bank2L, Bank3L and Bank4L are inputtedinto a plurality of data circuits provided to correspond to thefour-page data, respectively.

Also, when the level of TGB becomes “H” and the transfer gate TrNB isturned on, the program data on the memory cell CellB is transferred fromthe data circuit 2-i to the bit line BLB in the Lower bank.

If the program data is, for example, “0” (“0”-programming or programselect), the potential of the bit line BLB becomes Vss and if theprogram data is “1” (“1”-programming or write inhibit), the potential ofthe bit line BLB becomes the internal power supply potential Vdd (e.g.,about 2.3V).

(3) Step3

A program operation to the memory cell CellB in the Lower bank (thesupply of a program pulse) is executed.

First, the level of TGB is set at “L” and that of TGA is set at “H”.

At this time, the transfer gate TrNB is turned off and the bit line BLBis, therefore, electrically disconnected from the data circuit 2-i. Thebit line BLB turns into a floating state and the program data on thememory cell CellB is held by the bit line BLB.

Thereafter, a program pulse is supplied to the control gate line (wordline) of the memory cell CellB. At this moment, the potential of theselect gate line at the bit line BLB side is set at the internal powersupply potential Vdd and that of the select gate line at the source lineside is set at the ground potential Vss. Further, the potential of thecontrol gate line (selected word line) connected to the selected memorycell CellB is set at a program potential Vpgm and those of the othercontrol gate lines (unselected word lines) are set at a transferpotential Vpass.

In case of “0”-programming, the potential of the bit line BLB is Vss(0V) and that of the channel of the memory cell CellB is Vss, as well.Accordingly, in the memory cell CellB, a high electric field is appliedto the tunnel oxide film and an FN tunnel current flows into the tunneloxide film. That is, in the memory cell CellB, electrons are injectedfrom the channel into the floating gate electrode and the thresholdvoltage of the memory cell CellB, therefore, rises.

In case of “1”-programming, the potential of the bit line BLB is Vdd(e.g., about 2.3V), that of the channel of the memory cell CellB isVdd−Vth (where Vth is the threshold voltage of the select transistorconnected between the bit line and the memory cell), and the selecttransistor connected between the bit line and the memory cell is cutoff.

Therefore, in the memory cell CellB, if a program pulse is suppliedthereto, the channel potential also rises to, for example, about 8V bythe capacitive coupling between the word line and the channel. Due tothis, a high electric field is not applied to the tunnel oxide film andan FN tunnel current does not flow into the tunnel oxide film. In otherwords, the threshold voltage of the memory cell CellB has no change (theerase state is maintained).

While programming the memory cell CellB in the Lower bank, the programdata on the memory cell CellA held by the bit line BLA in the Upper bankis refreshed.

Namely, since the potential of TGA is “H” , the transfer gate TrNA isturned on and the bit line BLA is electrically connected to the datacircuit 2-i. The program data held by the bit line BLA is transferred toand held by the latch circuit in the data circuit 2-i. Then, the programdata held by the latch circuit is returned again to the bit line BLA(refresh).

The program data held by the bit line BLA in the Upper bank may berefreshed if there is a possibility that the potential of the bit lineBLA in the Upper bank (program data) changes because of leak current inthe Step2. In other words, in the Step2, i.e., while the program data onthe memory cell CellB is loaded and the program data on the memory cellCellB is held by the bit line BLB in the Lower bank, if the potential ofthe bit line BLA in the Upper bank has little change, it is notnecessary to carry out a refresh operation.

The refresh operation may be carried out before the program operation(the supply of a program pulse) or after the program operation (thesupply of a program pulse).

If the refresh operation is carried out after programming, the memorycell CellB is programmed in, for example, a state of Step2 (in which thelevel of TGA is “L” and that of TGB is “H”), i.e., a state in which thepotential of the bit line BLB is fixed to Vss (“0”-programming) or toVdd (“1”-programming) (in a non-floating state). Then, in a statechanged to a Step3 state (the level of TGA is “H” and that of TGB is“L”), the program data held by the bit line BLA may be refreshed.

Also, in this example, after the program data is transferred to the bitline BLA (in the Step1) and the program data is transferred to the bitline-BLB (in the Step2), the memory cell CellB in the Lower bank isprogrammed (in the Step3). However, if the potential change of the bitline (leak current) does not cause any problem, after the program datais transferred to the bit line BLA (in the Step1) and the program datais transferred to the bit line BLB (in the Step2), the memory cell CellAin the Upper bank may be programmed and then the memory cell CellB inthe Lower bank may be programmed. Alternatively, after the Step2, thememory cell CellA and the memory cell CellB may be programmed almostsimultaneously.

(4) Step4

After refreshing the program data held by the bit line BLA, the level ofTGA becomes “L” and the transfer gate TrNA is turned off. Thereafter,the level of TGB becomes “H” and the transfer gate TrNB is turned on.

After the level of TGA becomes “L”, a program operation (the supply of aprogram pulse) is executed to the memory cell CellA in the Upper bank.

Since the transfer gate TrNA is turned off, the bit line is in afloating state. Also, the program data on the memory cell CellA is heldby the bit line BLA.

Then, a program pulse is supplied to the control gate line (word line)of the memory cell CellA. At this moment, the potential of the selectgate line at the bit line BLA side is set at the internal power supplypotential Vdd, and the potential of the select gate line at the sourceline side is set at the ground potential Vss. Further, the potential ofthe control gate line (selected word line) connected to the selectedmemory cell CellA is set at the program potential Vpgm and those of theother control gate lines (unselected word lines) are set at the transferpotential Vpass.

In case of “0”-programming, the potential of the bit line BLA is Vss(0V) and that of the memory cell CellA is Vss. Accordingly, in thememory cell CellA, a high electric field is applied to the tunnel oxidefilm and an FN tunnel current flows into the tunnel oxide film. Namely,in the memory cell CellA, electrons are injected into the floating gateelectrode from the channel and the threshold voltage of the memory cellCellA, therefore, rises.

In case of “1”-programming, the potential of the bit line BLA is Vdd,that of the channel of the memory cell CellA is Vdd−Vth (where Vth isthe threshold voltage of the select transistor connected between the bitline and the memory cell) and the select transistor connected betweenthe bit line and the memory cell is cut off. In that case, if a programpulse is supplied to the memory cell, the channel potential rises to,for example, about 8V by the capacitive coupling between the word lineand the channel. Due to this, no FN tunnel current flows into the tunneloxide film and the threshold voltage of the memory cell CellA has nochange (the erase state is maintained).

While the memory cell CellA in the Upper bank is being programmed, anoperation for transferring program data on the memory cell CellB held bythe bit line BLB to the data circuit is first conducted in the Lowerbank.

Namely, if the level of TGB becomes “H” and the transfer gate TrNB isturned on, the bit line BLB is electrically connected to the datacircuit 2-i. Accordingly, the program data held by the bit line BLB isheld by the latch circuit (e.g., LATCH1 shown in FIG. 62) in the datacircuit 2-i.

(5) Step5

After transferring the program data held by the bit line BLB to thelatch circuit in the data circuit, a verify read operation is conductedto the memory cell CellB in the Lower bank. It is noted that at thismoment, the memory cell CellA in the Upper bank, for example, is beingprogrammed.

First, the verify read operation is conducted to the memory cell CellBin the Lower bank. Namely, since the level of the TGB is “H” and thetransfer gate TrNB is turned on, the bit line BLB is electricallyconnected to the data circuit 2-i.

Therefore, if the two select gate lines are applied with Vread, thecontrol gate line (selected word line) of the memory cell CellB isapplied with a read potential Vcgv0 for the verify read operation andthe unselected word lines are applied with a potential Vread with whichthe memory cells are always turned on, then the data of the memory cellCellB is transferred to the data circuit by way of the bit line BLB.

Thereafter, in the data circuit, an operation for detecting whether ornot precise data has been completely written into the memory cell CellBand an operation for generating reprogram data, are carried out based onthe data of the memory cell CellB and the program data held by the latchcircuit.

If it is judged that precise data has been completely written into thememory cell CellB, the later program operation to the memory cell CellBis completed (to be specific, in case of “0”-programming, the programdata is changed from “0” to “1” to prevent “0”-programming from beingconducted thereafter). On the other hand, if it is judged that precisedata has not been sufficiently written into the memory cell CellB, theprogram operation to the memory cell CellB continues.

After completing the above-stated verify operation, the reprogram datagenerated by the data circuit is transferred to and held by the bit lineBLB in the Lower bank.

(6) Step6

After completing the verify operation to the memory cell CellB, thelevel of TGB becomes “L” and the transfer gate TrNB is turned off. Then,the level of TGA becomes “H” and the transfer gate TrNA is turned on.

After the level of TGB becomes “L”, a reprogram (Re-write) operation isconducted to the memory cell CellB in the Lower bank.

In case of “0”-programming, if the program is, for example, deficient,“0” data is reprogrammed (re-written). If the program is alreadysufficient, the program data is changed to “1” to thereby prevent“0”-programming from being conducted.

Since the transfer gate TrNB is turned off, the bit line BLB is in afloating state. Further, the program data on the memory cell CellB isheld by the bit line BLB.

Thereafter, a program pulse is supplied to the control gate line (wordline) of the memory cell CellB.

On the other hand, while the memory cell CellB in the Lower bank isbeing programmed, an operation for transferring the program data on thememory cell CellA held by the bit line BLA to the data circuit, is firstcarried out.

Namely, if the level of TGA becomes “H” and the transfer gate TrNA isturned on, the bit line is electrically connected to the data circuit2-i. Accordingly, the program data held by the bit line BLA is held bythe latch circuit (e.g., LATCH1 shown in FIG. 62) in the data circuit2-i.

(7) Step7

After transferring the program data held by the bit line BLA to thelatch circuit in the data circuit, a verify operation to the memory cellCellA in the Upper bank is carried out. It is noted that at this moment,the program operation to, for example, the memory cell CellB iscontinuing in the Lower bank.

First, a verify read operation to the memory cell CellA in the Upperbank is carried out. Namely, since the level of TGA is “H” and thetransfer gate TrNA is turned on, the bit line BLA is electricallyconnected to the data circuit 2-i.

Accordingly, if the two select gate lines are applied with Vread, thecontrol gate line (selected word line) of the memory cell CellA isapplied with the read potential Vcgv0 for the verify read operation andunselected word lines are applied with the potential Vread with whichcorresponding memory cells are always turned on, then the data of thememory cell CellA is transferred to the data circuit by way of the bitline BLA.

Thereafter, in the data circuit, an operation for detecting whether ornot precise data has been completely written into the memory cell CellAand an operation for generating reprogram (Re-write) data, are carriedout based on the data of the memory cell CellA and the program data heldby the latch circuit.

If it is judged that precise data has been completely written into thememory cell CellA, the later program operation to the memory cell CellAis completed (to be specific, in case of “0”-programming, the programdata is changed from “0” to “1” to thereby prevent “0”-programming frombeing conducted later). On the other hand, if it is judged that precisedata has not been sufficiently written into the memory cell CellA, theprogram operation to the memory cell CellA continues.

After completing the above-stated verify operation, the reprogram(Re-write) data generated by the data circuit is transferred to and heldby the bit line BLA in the Upper bank.

(8) After Step7

Thereafter, the Step4 operation is executed again. Namely, after thestep7, the operations of Step4 to Step7 are repeatedly carried out untilall the memory cells including the memory cells CellA and CellB havebeen sufficiently programmed or until the number of program timesexceeds a predetermined number to cause a program defect.

In FIG. 62, while the program operations are conducted to the memorycells CellA and CellB, respectively, the potentials of, for example, thebit lines BLC and BLD are fixed to Vdd (during the program operations)or Vss (during the verify operations).

As in the case of the above-stated operation, program operations to thememory cells CellC and CellD are conducted. At this time, the potentialsof the bit lines BLA and BLB are fixed to Vdd (during the programoperations) or Vss (during the verify operations).

3.-4. Description of Respective Operations constituting ProgramOperation

Next, the respective operations constituting the above-stated programoperation will be described in detail.

It is assumed that a data circuit and a memory cell array haveconstitutions shown in FIG. 62. It is also assumed that the memory cellsCellA and CellB are programmed and that the potentials of the bit linesBLC and BLD are fixed to Vdd or Vss.

3.-4.-1. Data Load

In the “Step1” shown in FIG. 63, the program data on the memory cellCellA in the Upper bank is transferred from externally of the chip tothe data circuit and transferred from the data circuit to the bit lineBLA.

FIG. 64 shows timing for respective signals for executing the operationof the “Step1”.

First, the level of CSL becomes “H” and program data is inputted intothe latch circuit LATCH1 in the data circuit 2-i from externally of thechip through IO and nIO. At period Td1, the potentials of TRS and TGAbecome Vsg (e.g., about 4V) and the program data held by the latchcircuit LATCH1 is transferred to the bit line BLA in the Upper bank. Thepotentials of all of TGB, TGC and TGD are Vss.

In case of “0”-programming (program select), the program data held bythe latch circuit LATCH1 becomes “0” (N1=Vss, N2=Vdd). During“0”-programming, therefore, the bit line holds Vss (program data “0”).

In case of “1”-programming (write inhibit), the program data held by thelatch circuit LATCH1 becomes “1” (N1=Vdd, N2=Vss). During“1”-programming, therefore, the bit line BLA holds Vdd (program data“1”).

Then, at period Td2, the potentials of TRS and TGA become Vss and dataload for loading program data on the memory cell CellA is completed.

During the above-stated data load, the potential of VSC is set at, forexample, Vss and that of PREG is set at Vsg or Vdd. In that case, thepotential of the bit line BLC is fixed to Vss and the capacitivecoupling noise between the bit lines to the bit line BLA can beeliminated. The potential of BLC (VSC) may be changed from Vss to Vdd.

In the “Step2” shown in FIG. 63, the program data on the memory cellCellB in the Lower bank is inputted from externally of the chip into thedata circuit and transferred from the data circuit to the bit line BLB.

FIG. 65 shows timing for respective signals for executing “Step2”operation.

First, the program data is inputted into the latch circuit LATCH1 in thedata circuit 2-i from externally of the chip through nodes Naij andNbij. At period Td1, the potentials of TRS and TGB become Vsg (e.g.,about 4V) and the program data held by the latch circuit LATCH1 istransferred to the bit line BLB in the Lower bank. The potentials of allof TGA, TGC and TGD are Vss.

Then, at period Td2, the potentials of TRS and TGB become Vss and thedata load for loading program data on the memory cell CellB iscompleted.

During the above-stated data load, the potential of VSD is set at, forexample, Vdd and that of PRED is set at Vsg. In this case, the potentialof the bit line BLD is fixed to Vdd and the capacitive coupling noisebetween bit lines to the bit line BLB can be eliminated.

3.-4.-2. Supply of Program Pulse

In the “Step3” show in FIG. 63, a program pulse is supplied to thememory cell CellB in the Lower bank.

FIG. 66 shows timing for respective signals for executing “Step3”operation (operation relating to the supply of a program pulse).

The potentials of TGB, TGC and TGD are all Vss and the transfer gateTrNB, TrNC and TrND are turned off.

The potential of PREB is Vss and the bit line BLB holds the program dataso as to program the memory cell CellB. The potential of the bit lineBLD is fixed to Vdd. That is, the potential of PRED is set at Vsg andthat of VSD is set at Vdd.

Since the bit line BLA holds program data on the memory cell CellA, thepotential of PREA is set at Vss.

First, at period Tpr1, the potential of the select gate line SG1Lbecomes Vdd. At period Tpr2, the potentials of unselected control gatelines (word lines) CG2L to CG16L become the transfer potential Vpass. Atperiod Tpr3, the potential of the selected control gate line (word line)CG1L becomes the program potential Vpgm.

In case of “0”-programming, the potential of the bit line BLB is Vss(“0” data is held) and the channel of the memory cell CellB, therefore,becomes Vss (0V), as well. Accordingly, in the memory cell CellB, a highelectric field is applied to the tunnel oxide film and electrons areinjected from the channel into the floating gate electrode.

In case of “1”-programming, the potential of the bit line-BLB is Vdd(“1” data is held) and the channel of the memory cell CellB, therefore,becomes Vdd−Vth (where Vth is the threshold voltage of the selecttransistor). Also, the select transistor is cut off and the channel ofthe memory cell CellB turns into a floating state.

In this case, in the memory cell CellB, the channel potential rises to,abbot 8V by the capacitive coupling between the control gate line (wordline) and the channel. Due to this, a high electric field is not appliedto the tunnel oxide film and no electrons are injected from the channelinto the floating gate electrode.

Then, at period Tpr4, the potential of the selected control gate lineCG1L decreases from the program potential Vpgm to the ground potentialVss. At period Tpr5, the potentials of the unselected control gate linesCG2L to CG16L decrease from the transfer potential Vpass to the groundpotential Vss. Further, at period Tpr6, the potential of the select gateline SG1L decreases from Vdd to Vss.

Through the above procedures, the supply of a program pulse iscompleted.

In an ordinary program operation, after the completion of the supply ofa program pulse, the bit line BLB is discharged. In the presentinvention, however, after the completion of the supply of a programpulse, the bit line BLB is not discharged. This is because the bit lineBLB holds the program data in the present invention.

3.-4.-3. Refresh

In the “Step3” shown in FIG. 63, while a program pulse is being appliedto the memory cell CellB in the Lower bank, the program data held by thebit line BLA in the Upper bank is refreshed.

FIG. 67 shows timing for respective signals for executing “Step3”operation (operation relating to the refresh operation to the programdata).

The potentials of TGB, TGC and TGD are all Vss and the transfer gateTrNB, TrNC and TrND are turned off.

The potential of PREA is set at Vss so as to refresh the program data onthe memory cell CellA held by the bit line BLA. Since the memory cellCellB is programmed, the potential of PREB is also Vss. Further, thepotentials of PREC and PRED are set at Vsg, those of VSc and VSD are setat Vdd and the those of the bit lines BLC and BLD are fixed to Vdd.

First, at period Trf1, the potentials of SEN and LAT become Vss and theclocked inverters INV1 and INV2 turn into a non-operation state. Namely,the latch circuit LATCH1 turns into a non-operation state. At periodTrf2, the potentials of TRS and TGA become Vsg and the bit line BLA inthe Upper bank is electrically connected to the latch circuit LATCH1 inthe data circuit 2-i.

As a result, the program data held by the bit line BLA is transferred tothe sense node N1. Thereafter, at period Trf3, when the potential of SENbecomes Vdd and the clocked inverter INV1 turns into an operation state,the clocked inverter INV1 senses the potential of the sense node N1(program data).

At period Trf4, when the potential of LAT becomes Vdd, the clockedinverter INV2 turns into an operation state and the program data islatched by the latch circuit LATCH1. That is, the program data held bythe bit line BLA is amplified by the latch circuit LATCH1.

In addition, since the latch circuit LATCH1 is electrically connected tothe bit line BLA, the program data latched by the latch circuit LATCH1is returned to the bit line BLA again (refresh).

At period Trf5, the potentials of TRS and TGA become Vss and the refreshoperation to the program data held by the bit line BLA is completed.

3.-4.-4. Supply of Program Pulse

In the “Step4” and “Step5” shown in FIG. 63, a program pulse is suppliedto the memory cell CellA in the Upper bank.

FIG. 68 shows timing for respective signals for executing “Step4” and“Step5” operations (operations relating to the supply of a programpulse).

The potentials of TGA, TGC and TGD are all Vss and the transfer gatesTrNA, TrNC and TrND are turned off. Due to the need to conduct programdata transfer and verify read operation to be described later, thepotential of TGB is set at Vsg.

The potential of PREA is set at Vss so as to program the memory cellCellA and the bit line BLA holds program data. The potential of PREC isset at Vsg, that of VSc is set at Vdd and that of the bit line BLC isfixed to Vdd. Also, the potential of PREB is set at Vss.

First, at period Tpr1, the potential of the select gate line SG1Ubecomes Vdd. At period Tpr2, the potentials of the unselected controlgate lines (word lines) CG2U to CG16U become the transfer potentialVpass. At period Tpr3, the potential of the selected control gate line(word line) CG1U becomes the program potential Vpgm.

In case of “0”-programming, the potential of the bit line BLA is Vss(“0” data is held) and the channel of the memory cell CellA, therefore,becomes Vss (0V). Accordingly, in the memory cell CellA, a high electricfield is applied to the tunnel oxide film and electrons are injectedfrom the channel into the floating gate electrode.

In case of “1”-programming, the potential of the bit line BLA is Vdd(“1” data is held) and the channel of the memory cell CellA, therefore,becomes Vdd−Vth (where Vth is the threshold voltage of the selecttransistor). Further, the select transistor is cut off and the channelof the memory cell CellA turns into a floating state.

In this case, in the memory cell CellA, the channel potential rises to,for example, about 8V by the capacitive coupling between the controlgate electrode (word line) and the channel. Due to this, a high electricfield is not applied to the tunnel oxide film and no electrons areinjected from the channel into the floating gate electrode.

Then, at period Tpr4, the potential of the selected control gate lineCG1U decreases from the program potential Vpgm to the ground potentialVss. At period Tpr5, the potentials of the unselected control gate linesCG2U to CG16U decrease from the transfer potential Vpass to the groundpotential Vss. At period Tpr6, the potential of the select gate lineSG1U decreases from Vdd to Vss.

Through the above-stated procedures, the supply of a program pulse tothe memory cell CellA is completed. In the present invention, after thecompletion of the supply of a program pulse, the bit line BLA is notdischarged. This is because the bit line BLA holds the program data inthe present invention.

3.-4.-5. Program Data Transfer

In the “Step4” shown in FIG. 63, while a program pulse is being suppliedto the memory cell CellA in the Upper bank, an operation fortransferring the program data held by the bit line BLB to the latchcircuit LATCH1 in the data circuit 2-i, is first carried out in theLower bank.

FIG. 69 shows timing for respective signals for executing “Step4”operation (operation relating to program data transfer).

The potentials of TGA, TGC and TGD are all Vss and the transfer gatesTrNA, TrNC and TrND are turned off.

The potential of PREB is set at Vss so as to transfer the program dataon the memory cell CellB held by the bit line BLB. Since the memory cellCellA is programmed, the potential of PREA is also Vss. Further, thepotentials of PREC and PRED are set at Vsg, those of VSc and VSD are setat Vdd and those of the bit lines BLC and BLD are set at Vdd.

First, at period Tts1, the potentials of SEN and LAT become Vss and theclocked inverters INV1 and INV2 turn into a non-operation state. Thatis, the latch circuit LATCH1 turns into a non-operation state. Further,at period Tts2, the potentials of TRS and TGB become Vsg and the bitline BLB in the Lower bank is electrically connected to the latchcircuit LATCH1 in the data circuit 2-i.

As a result, the program data held by the bit line BLB is transferred tothe sense node N1. Then, at period Tts3, when the potential of SENbecomes Vdd and the clocked inverter turns into an operation state., theclocked inverter INV1 senses the potential of the sense node N1 (programdata).

Thereafter, at period Tts4, when the potential of TRS changes from Vsgto Vss, the transistor TN31 is turned off and the latch circuit LATCH1is electrically disconnected from the bit line BLB.

At period Tts5, when the potential of LAT becomes Vdd, the clockedinverter INV2 turns into an operation state and the program data islatched by the latch circuit LATCH1. That is, the program data held bythe bit line BLB is latched by the latch circuit LATCH1.

At period Tts6, the potential of TGB becomes Vss and the transfer of theprogram data held by the bit line BLB is completed.

3.-4.-6. Verify Read

In the “Step5” shown in FIG. 63, while a program pulse is being suppliedto the memory cell CellA in the Upper bank, a verify read operation isconducted to the memory cell CellB in the Lower bank.

FIG. 70 shows timing for respective signals for executing “Step5”operation (operation relating to the verify read operation).

The potentials of TGA, TGC and TGD are all Vss and the transfer gatesTrNA, TrNC and TrND are turned off.

The potential of PREA is set at Vss so as to program the memory cellCellA. The potential of the bit line BLC is set at Vdd and that of thebit line BLD is set at Vss. The potentials of PREC and PRED are,therefore, set at Vsg, that of VSc is set at Vdd and that of VSD is setat Vss.

First, at period Tvfy1, the potential of TGB becomes Vsg. Also, thepotential of PREB becomes Vpre (e.g., about 3V) and the bit line BLB isprecharged with about 1.8V. Then, at period Tvfy2, the potential of PREBbecomes Vss and the precharge of the bit line BLB is completed.

At period Tvfy3, the potential of the selected control gate line (wordline) CG1L is set at the read potential Vcgv0 for the verify readoperation (e.g., about 0.5V) and those of the select gate lines SG1L andSG2L and the control gate lines (word lines) CG2L to CG16 are set at thepotential Vread (e.g., about 3.5V) with which corresponding memory cellsare always turned on.

At this moment, the potential of the bit line BLB changes or ismaintained according to the data of the memory cell CellB.

For example, as for the memory cell CellB, if “0”-programming isdeficient and “1”-programming is conducted, the threshold voltage of thememory cell CellB is lower than Vcgv0. Due to this, the memory cellCellB is turned on and the charges of the bit line BLB are discharged.As a result, the potential of the bit line BLB becomes Vss.

Further, as for the memory cell CellB, if “0”-programming is sufficient,the threshold voltage of the memory cell CellB is higher than Vcgv0. Dueto this, the memory cell CellB is turned off and the charges of the bitline BLB are not discharged. As a result, the bit line BLB maintains theprecharge potential (e.g., about 1.8V).

Then, at period Tvfy4, the potentials of the control gate lines (wordlines) CG1L to CG16L and the select gate lines SG1L and SG2L are set atVss (0V).

At period Tvfy5, when the level of VFY becomes “L”, the transistor TP32is turned on. Due to this, the potential of the bit line BLB isdetermined according to the program data latched by the latch circuitLATCH1.

In case of “1”-programming (write inhibit), for example, since the latchcircuit LATCH1 latches the program data “1” (the level of the node N2 is“L”), the transistor TP31 is turned on and the potential of the bit lineBLB is fixed to Vdd.

Namely, by period Tvfy4, the potential of the bit line BLB becomes Vssdue to the verify read operation. At period Tvfy5, the potential of thebit line BLB is forcedly set at Vdd.

In addition, in case of “0”-programming (program select), since thelatch circuit LATCH1 latches the program data “0” (the level of the nodeN2 is “H”), the transistor TP31 is turned off. Accordingly, the bit lineBLB maintains the data read to the bit line BLB by the verify readoperation, i.e., the potential of the bit line BLB at period Tvfy4 as itis.

That is, if “0”-programming is deficient, the potential of the bit lineBLB becomes Vss. If “0”-programming is sufficient, the potential of thebit line BLB becomes the precharge potential.

Then, at period Tvfy6, the potentials of SEN and LAT become Vss and theclocked inverters INV1 and INV2 turn into a non-operation state, i.e.,the latch circuit LATCH1 turns into a non-operation state. At thismoment, the program data latched by the latch circuit LATCH1 iseliminated.

At period Tvfy7, when the potential of TRS becomes Vsg, the transistorTN31 is turned on and the bit line BLB is electrically connected to thelatch circuit LATCH1. At period Tvfy3, the level of SEN becomes “H” andthe clocked inverter INV1 senses the potential of the bit line BLB.Further, at period Tvfy9, when the level of LAT becomes “H”, thepotential of the bit line BLB is latched by the latch circuit LATCH1.

Namely, the potential of the bit line BLB is latched, As reprogram(Re-write) data, by the latch circuit LATCH1. At the same time, thereprogram (Re-write) data is transferred to and held by the bit lineBLB.

Thereafter, the reprogram (Re-write) operation is carried out based onthe reprogram (Re-write) data held by the bit line BLB.

Meanwhile, in principle, the program operation (the supply of a programpulse) is completed when the potentials of bit lines BLB correspondingto all columns (all selected memory-cells) become “H” as a result of theverify read operation. If there exists a column in which the potentialof the bit line BLB is “L”, i.e., there exists a memory cell for which“0”-programming is deficient, then, the program operation continuesunless the number of program times reaches the upper limit.

The detection as to whether or not the potentials of the bit lines BLBof all columns become “H” may be made by using a batch detection circuit(e.g., as shown in FIGS. 8, 9 and 12) (Program completion detection).

Finally, at period Tvfy10, the potentials of TRS and TGA become Vss andthe verify read operation is completed.

3.-4.-7. Others

In the “Step6” and “Step7” shown in FIG. 63, the same operations asthose in “Step4” and “Step5” are carried out. Namely, in the Lower bank,a program pulse is supplied to the memory cell CellB. In the Upper bank,the program data held by the bit line BLA is transferred and the verifyread operation is conducted to the memory cell CellA.

The respective operations of the supply of a program pulse, the transferof program data and the verify read operation in the “Step6” and “Step7”are exactly the same as the respective operations in “Step4” and “Step5”(see Section 3.-4.-4, 3.-4.-5. And 3.-4.-6) except for the difference oftargets. Only waveform views are shown in FIGS. 71 to 73 and detaileddescription will not be, therefore, given to those operations.

In the above-stated example, after the bit line is turned into afloating state, a program pulse is supplied to the memory cell.Conversely, after a program pulse is supplied to the memory cell, thebit line may be turned into a floating state to allow the bit line tohold the program data.

4. Concrete Example 2

In Concrete Example 1 stated above, it is assumed that a plurality ofmemory cells (selected bit lines) connected to one data circuit andprogrammed simultaneously are arranged in different banks. Due to this,the control gates (word lines) of the plurality of selected memory cellsare not common to the memory cells.

In this example, description will be given to a case where a pluralityof memory cells existing in a single bank (i.e., a control gate line iscommon to the memory cells) are programmed simultaneously using one datacircuit. Needless to say, only a storage circuit (e.g., a latch circuit)capable of temporarily holding program data (two-level data ormulti-level data) on one memory cell is arranged in one data circuit.

4.-1. Overview

In this embodiment, description will be given hereinafter while taking atwo-level NAND type flash memory as an example, as in the case ofConcrete Example 1.

The same chip layout and data circuit as those in Concrete Example 1 areemployed (see FIGS. 61 and 62). The connection between the data circuitand the bit lines, however, satisfies the relationship shown in, forexample, FIG. 74. That is to say, six bit lines BLA1, BLA2, BLA3, BLB1,BLB2 and BLB3 are connected to one data circuit 2-i.

Among the six bit lines BLA1, BLA2, BLA3, BLB1, BLB2 and BLB3, the threebit lines BLA1, BLA2 and BLA3 are arranged in an Upper bank and thethree bit lines BLB1, BLB2 and BLB3 are arranged in a Lower bank.

In this example, using one data circuit 2-i, three memory cells CellA1,CellA2 and CellA3 connected to the three bit lines BLA1, BLA2 and BLA3in the Upper bank, respectively, and having a common control gate lineCGlU1, are programmed simultaneously. At this time, the three bit linesBLB1, BLB2 and BLB3 in the Lower bank are used to make program data onthe memory cells CellA, CellA2 and CellA3 to temporarily wait,respectively.

Further, three memory cells CellB1, CellB2 and CellB3 connected to thethree bit lines BLB1, BLB2 and BLB3 in the Lower bank, respectively andhaving a common control gate line CGlL1, are programmed simultaneously.At this time, the three bit lines BLA1, BLA2 and BLA3 in the Upper bankare used to make the program data on the memory cells CellB1, CellB2 andCellB3, respectively temporarily wait.

4.-2. Program Operation

The program operation will be described concretely hereinafter withreference to FIGS. 75 to 77. The program operations to the memory cellsCellA1, CellA2 and CellA3 are exactly the same as those to the memorycells CellB1, CellB2 and CellB3 except for the difference of targets.Therefore, description will be given only to the program operations tothe memory cells CellA1, CellA2 and CellA3.

(1) Step1-1

First, Data Load for loading program data on the memory cell CellA1 iscarried out.

Program data on the memory cell CellA1 is inputted from externally of achip into a data circuit 2-i. Then, when the level of TGA1 becomes “H”,a transfer gate TrNA1 is turned on. Due to this, the program data in thedata circuit 2-i is transferred to and held by the bit line BLA1. Atthis time, the level of TGB1 is “L” and a transfer gate TrNB1 is turnedoff.

In case of “0”-programming (program select), the program data is “0” andthe potential of the bit line BLA1 becomes 0V. In case of“1”-programming (write inhibit), the program data is “1” and thepotential of the bit line BLA1 becomes Vdd.

Thereafter, the level of TGB1 changes from “L” to “H” and the transfergate TrNB1 is turned on. Therefore, the program data in the data circuit2-i is also transferred to and held by the bit line BLB1.

Step1-2

Following Step1-1, Data Load for loading program data on the memory cellCellA2 is carried out.

First, the levels of TGA1 and TGB1 are set at “L” and the transfer gatesTrNA1 and TrNB1 are turned off. At this time, the bit lines BLA1 andBLB1 turn into a floating state and the program data on the memory cellCellA1 is enclosed in the bit lines BLA1 and BLB1.

Thereafter, program data on the memory cell CellA2 is inputted fromexternally of the chip into the data circuit 2-i. Then, when the levelof TGA2 becomes “H”, the transfer gate TrNA2 is turned on. Therefore,the program data in the data circuit 2-i is transferred to and held bythe bit line BLA2. At this time, the level of TGB2 is “L” and thetransfer gate TrNB2 is turned off.

Then, the level of TGB2 changes from “L” to “H” and the transfer gateTrNB2 is turned on. Therefore, the program data in the data circuit 2-iis also transferred to and held by the bit line BLB2.

(3) Step1-3

Following the Step1-2, Data Load for loading program data on the memorycell CellA3 is carried out.

First, the levels of TGA2 and TGB2 are set at “L” and the transfer gatesTrNA2 and TrNB2 are turned off. At this time, the bit lines BLA2 andBLB2 turn into a floating state and the program data on the memory cellCellA2 is enclosed in the bit lines BLA2 and BLB2.

Thereafter, program data on the memory cell CellA3 is inputted fromexternally of the chip into the data circuit 2-i. Then, when the levelof TGA3 becomes “H”, the transfer gate TrNA3 is turned on. Therefore,the program data in the data circuit 2-i is transferred to and held bythe bit line BLA3. At this time, the level of TGB3 is “L” and thetransfer gate TrNB3 is turned off.

Thereafter, the level of TGB3 changes from “L” to “H” and the transfergate TrNB3 is turned on. Therefore, the program data in the data circuit2-i is also transferred to and held by the bit line BLB3.

(4) Step1-4

Data Load for loading program data has been completed by the operationsin “Step1-1” to “Step1-3”. Thereafter, in this example, write data heldby each bit line is refreshed before applying a program pulse.

However, the refresh operation to the write data (“Step1-4” and“Step1-5”) may be conducted if there is a possibility that the potentialof bit line for which Data Load has been already completed, changes witha leak current during Data Load. If there is no possibility that thepotential of the bit line for which Data Load has been alreadycompleted, does not change with the leak current, it is not necessary toconduct the refresh operation to the write data.

In that case, after the completion of Data Load (in “Step1-1” to“Step1-3”), a program pulse is instantly applied (in “Step1-6”).

If the potential change of the bit line due to the leak current causes aproblem, a program data refresh operation is conducted to the programdata on the memory cell CellA1 held by the bit lines BLA1 and BLB1 andthe program data on the memory cell CellA2 held by the bit lines BLA2and BLB2.

Namely, the program data on the memory cell CellA3 held by the bit linesBLA3 and BLB3 is not refreshed even if the potential change of the bitline due to the leak current causes a problem. This is because Data Loadfor loading the program data on the memory cell CellA3 is finallyconducted (in “Step1-3”) and time (Data retention time) for which thebit lines BLA3 and BLB3 hold the program data is, therefore, short.

In “Step1-4”, the program data on the memory cell CellA1 is refreshed.

First, the level of TGA1 becomes “H” and the transfer gate TrNA1 isturned on. At this time, the bit line BLA1 is electrically connected tothe data circuit 2-i. Thus, using the latch circuit in the data circuit2-i, the program data on the memory cell CellA1 held by the bit lineBLA1 is refreshed.

While refreshing the program data held by the bit line BLA1, the levelof TGB1 is “L” and the transfer gate TrNB1 is turned off.

Then, the level of TGA1 becomes “L” and the transfer gate TrNA1 isturned off. Further, the level of TGB1 becomes “H” and the transfer gateTrNB1 is turned on. At this time, the bit line BLB1 is electricallyconnected to the data circuit 2-i. Thus, using the latch circuit in thedata circuit 2-i, the program data on the memory cell CellA1 held by thebit line BLB1 is refreshed.

(5) Step1-5

In “Step1-5”, the program data on the memory cell CellA2 is refreshed.

First, the level of TGA2 becomes “H” and the transfer gate TrNA2 isturned on. At this time, the bit line BLA2 is electrically connected tothe data circuit 2-i. Thus, using the latch circuit in the data circuit2-i, the program data on the memory cell CellA2 held by the bit lineBLA2 is refreshed.

While refreshing the program data held by the bit line BLA2, the levelof TGB2 is “L” and the transfer gate TrNB2 is turned off.

Then, the level of TGA2 becomes “L” and the transfer gate TrNA2 isturned off. Further, the level of TGB2 becomes “H” and the transfer gateTrBN2 is turned on. At this time, the bit line BLB2 is electricallyconnected to the data circuit 2-i. Thus, using the latch circuit in thedata circuit 2-i, the program data on the memory cell CellA2 held by thebit line BLB2 is refreshed.

During “Step1-1” to “Step1-5”, the select gate lines SG1U1 and SG1L1 areturned off. The write data held by each bit line is not, therefore,eliminated.

(6) Step1-6

In “Step1-6”, a program pulse is supplied.

The bit line BLA1 already holds the program data on the memory cellCellA1, the bit line BLA2 already holds the program data on the memorycell CellA2 and the bit line BLA3 already holds the program data on thememory cell CellA3. Due to this, if a program pulse is supplied to thecontrol gate line CGlU1, program operations to the three memory cellsCellA1, CellA2 and CellA3 are simultaneously executed.

The potentials of the control gate line (word line) and the select gatelines during the program operations are as follows.

The potential of the select gate line SG1U1 at the bit line side is setat Vdd, that of the select gate line at the source line side is set atVss, that of the selected control gate line CG1U1 is set at the programpotential Vpgm and those of unselected control lines are set at thetransfer potential Vpass.

In case of “0”-programming (program select), the potential of thechannel of the selected memory cell becomes 0V. Due to this, a highelectric field is applied to the tunnel oxide film and electrons areinjected from the channel into the floating gate electrode.

In case of “1”-programming (write inhibit), the potential of the channelof the selected memory cell becomes Vdd−Vth (where Vth is the thresholdvoltage of the select transistor) and the select transistor at the bitline side is turned off. Thus, the channel turns into a floating state.

Accordingly, if a program pulse is supplied, the channel potential risesto about 8V by the capacitive coupling between the control gate line andthe channel. Namely, no electric field is applied to the tunnel oxidefilm and no electrons are injected from the channel into the floatinggate electrode.

(7) Step1-7

After the completion of the supply of a program pulse, an operation fortransferring the program data temporarily stored in the bit line to thedata circuit, a verify operation (verify read operation and Programcompletion detection) and an operation for transferring reprogram(Re-write) data to the bit line, are carried out.

Since the data circuit 2-i has only one latch circuit capable oftemporarily storing program/read data on one memory cell, theseoperations are carried out for each bit line (or memory cell).

In this example, the operation for transferring the program datatemporarily stored in the bit line BLB1 (which may be BLA1) to the datacircuit, the verify read operation (including Program completiondetection) to the memory cell CellA1, and the operation for transferringreprogram (Re-write) data to the bit line BLB1 (which may be BLA1 orBLB1), are carried out in “Step1-7” and “Step1-8”.

Further, in “Step1-9” and “Step1-10”, the operation for transferring theprogram data temporarily stored in the bit line BLB2 (not the bit lineBLA2, which will be described later) to the data circuit, the verifyread operation (including Program completion detection) to the memorycell CellA2 and the operation for transferring reprogram (Re-write) datafrom the data circuit to the bit line BLB2 (which may be BLA2 or BLB2),are carried out.

In “Step1-11” and “Step1-12”, the operation for transferring the programdata temporarily stored in the bit line BLB3 (not the bit line BLA3,which will be described later) to the data circuit, the verify readoperation (including Program completion detection) to the memory cellCellA3 and the operation for transferring reprogram (Re-write) data fromthe data circuit to the bit line BLB3 (which may be BLA3 or BLB3), arecarried out.

In this example, the program data on the selected memory cell in theUpper bank is held by the bit line connected to the memory cell and byone bit line in the Lower bank. The reason is as follows. In the verifyread operation to be described later, if a verify read operation isconducted to, for example, the selected memory cell CellA1, program dataheld by the bit lines BLA2 and BLA3 connected to the other selectedmemory cells CellA2 and CellA3, respectively, are eliminated.

Namely, if the program data on the bit lines BLB2 and BLB3 in the Lowerbank is held, the program data on the memory cells CellA2 and CellA3 areheld by the bit lines BLB2 and BLB3 and not eliminated even if theprogram data held by the bit lines BLA2 and BLA3 in the Upper-bank areeliminated during the verify read operation to the memory cell CellA1.

“Step1-7” operation will be described hereinafter.

In “Step1-7”, an operation for transferring the program data on thememory cell CellA in the Upper bank which data is held by the bit lineBLB1 in the Lower bank to the data circuit, is carried out.

First, when the level of TGB1 becomes “H”, the transfer gate TrNB1 isturned on. At this time, the bit line is electrically connected to thedata circuit and the program data on the memory cell CellA1 held by thebit line BLB1 in the Lower bank is transferred to the data circuit.

Alternatively, in this example, the level of TGA1 may be set at “H”, thetransfer gate TrNA1 may be turned on and the program data held by thebit line BLA1 in the Upper bank may be transferred to the data circuit.

The program data is held by the latch circuit LATCH1 in the data circuit2-i shown in, for example, FIG. 62.

(8) Step1-8

In “Step1-8”, a verify read operation to the memory cell CellA1 iscarried out.

First, the bit line BLA1 is precharged with a precharge potential (e.g.,about 1.8V). At this time, the program data held by the bit line BLA1 iseliminated. However, since the program data has been already transferredto the latch circuit in the data circuit, no problem arises.

Then, when th level of TGA1 is set at “H” and the transfer gate TrNA1 isturned on, the bit line BLA1 is electrically connected to the datacircuit.

If the two select gate lines are applied with Vread, the control gateline (selected word line) CGlU1 of the memory cell CellA1 is appliedwith the read potential Vcgv0 for the verify read operation andunselected word lines are applied with the potential Vread with whichcorresponding memory cells are always turned on, then the data of thememory cell CellA1 is transferred to the data circuit 2-i by way of thebit line BLA1.

Thereafter, in the data circuit 2-i, an operation for generatingreprogram (Re-write) data and an operation for detecting whether or notprecise data has been completely written into the memory cell CellA1(Program completion detection) are carried out based on the data of thememory cell CellA1 and the program data latched by the latch circuitLATCH1.

Providing that the data circuit shown in FIG. 62 is used, if“1”-programming and “0”-programming” are sufficient, the reprogram(Re-write) data becomes “1” and “0”-programming is not, therefore,conducted thereafter. Namely, the program operation to the memory cellCelA1 is completed.

If “0”-programming is deficient, the reprogram (Re-write) data becomes“0” and “0”-programming, therefore, continues. Namely, the programoperation to the memory cell CellA1 continues.

In the verify read operation to the memory cell CellA1, the readpotential Vcgv0 is applied to the control gate line CGlU1.

As a result, the memory cell A1 as well as the memory cells CellA2 andCellA3 having the control gate line CGlU1 common to the memory cell A1are turned on, and the program data on the memory cells CellA2 andCellA3 held by the bit lines BLA2 and BLA3 are eliminated. However, theprogram data on the memory cells CellA2 and CellA3 are also held by thebit lines BLB2 and BLB3 in the Lower bank and no problem, therefore,arises.

After the verify read operation, the reprogram (Re-write) data on thememory cell CellA1 is transferred to the bit line BLA1 (actually, sincethe transfer gate TrNA1 is turned on, the reprogram (Re-write) data istransferred to the bit line BLA1 almost simultaneously with the verifyread operation). At this time, the level of TGB1 is “L” and the transfergate TrNb1 is turned off.

Thereafter, when the level of TGB1 is set at “H”, the transfer gateTrNB1 is turned on and the reprogram (Re-write) data on the memory cellCellA1 is also transferred to the bit line BLB1.

As will be described later, during the verify operation to the memorycell CellA2, the reprogram (Re-write) data on the memory cells CellA1held by the bit line BLA1 is eliminated. Accordingly, the program dataheld by the bit line BLB1 is used in the later operation.

(9) Step1-9

As in the case of the above-stated “Step1-7” and “Step1-8” operations,“Step1-9” and “Step1-10” operations are carried out.

First, the “Step1-9” operation will be described.

In “Step1-9”, an operation for transferring the program data on thememory cell CellA2 in the Upper bank which data is held by the bit lineBLB2 in the Lower bank, to the data circuit, is carried out.

First, when the level of TGB2 becomes “H”, the transfer gate TrNB2 isturned on. At this time, the bit line BLB2 is electrically connected tothe data circuit and the program on the memory cell CellA2 held by thebit line BLB2 in the Lower bank is transferred to the data circuit.

In this example, the program data on the memory cell CellA2 held by thebit line BLA2 in the Upper bank is eliminated during the verify readoperation to the memory cell CellA1 (in the “Step1-8”). The program dataon the memory cell CellA2 is, therefore, transferred from the bit lineBLB2 in the Lower bank to the data circuit.

The program data is held by the latch circuit LATCH1 in the data circuit2-i shown in, for example, FIG. 62.

(10) Step1-10

In “Step1-10”, a verify read operation to the memory-cell CellA2 iscarried out.

First, the bit line BLA2 is precharged with the precharge potential(e.g., about 1.8V). Thereafter, when the level of TGA2 is set at “H” andthe transfer gate TrNA2 is turned on, the bit line BLA2 is electricallyconnected to the data circuit.

If the two select gate lines are applied with Vread, the control gateline (selected-word line) CGlU1 of the memory cell CelA2 is applied withthe read potential Vcgv0 for the verify read operation and unselectedword lines are applied with the potential Vread (e.g., about 3.5V) withwhich corresponding memory cells are always turned on, then the data ofthe memory cell CellA2 is transferred to the data circuit 2-i by way ofthe bit line BLA2.

Thereafter, an operation for generating reprogram (Re-write) data and anoperation for detecting whether or not precise data has been completelywritten into the memory cell CellA2 (Program completion detection), arecarried out.

For example, if “1”-programming is conducted and “0”-programming issufficient, the reprogram (Re-write) data becomes “1” and“0”-programming is not conducted to the memory cell CellA2 thereafter.Namely, the program operation to the memory cell CellA2 is completed.

If “0”-programming is deficient, the reprogram (Re-write) data becomes“0” and “0”-programming to the memory cell CellA2, therefore, continues.

In the verify read operation to the memory cell CellA2, the control gateline CGlU1 is applied with the read potential Vread.

As a result, the memory cell CellA2 as well as the memory cells CellA1and CellA3 having the control gate line CGlU1 common to the cellsCellA2, CellA1 and CellA3 are turned on, and the program data on thememory cells CellA1 and CellA3 held by the bit lines BLA1 and BLA3 areeliminated.

However, the program data (or reprogram (Re-write) data) on the memorycells CellA1 and CellA3 are held by the bit lines BLB1 and BLB3 in theLower bank, respectively, and these program data are not, therefore,completely eliminated.

After the verify read operation, the reprogram (Re-write) data on thememory cell CellA2 is transferred to the bit line BLA2 (actually, sincethe transfer gate TrNA2 is turned on, the reprogram (Re-write) data istransferred to the bit line BLA2 almost simultaneously with the verifyread operation). At this time, the level of TGB2 is “L” ad the transfergate TrNB2 is turned off.

Thereafter, when the level of TGB2 is set at “H”, the transfer gateTrNB2 is turned on and the reprogram (Re-write) data on the memory cellCellA2 is also transferred to the bit line BLB2.

As will be described later, during the verify read operation to thememory cell CellA3, the reprogram (Re-write) data on the memory cellCellA2 held by the bit line BLA2 is eliminated. The program data held bythe bit line BLB2 is, therefore, used in later operation.

(11) Step1-11

As in the case of the above-stated “Step1-9” and “Step1-10” operations,“Step1-11” and “Step1-12” operations are carried out.

First, “Step1-11” operation will be described.

In “Step1-11”, an operation for transferring program data on the memorycell CellA3 in the Upper bank which data is held by the bit line BLB3 inthe Lower bank to the data circuit, is carried out.

First, when the level of TGB3 becomes “H”, the transfer gate TrNB3 isturned on. At this time, the bit line BLB3 is electrical connected tothe data circuit and the program data on the memory cell CellA3 held bythe bit line BLB3 in the Lower bank is transferred to the data circuit.

The program data on the memory cell CellA3 held by the bit line BLA3 inthe Upper bank has been already eliminated during the verify readoperation to the memory cell CellA1 (in “Step1-8”). The program data onthe memory cell CellA3 is, therefore, transferred from the bit line BLB3in the Lower bank to the data circuit.

This program data is held by the latch circuit LATCH1 in the datacircuit 2-i shown in, for example, FIG. 62.

(12) Step1-12

In “Step1-12”, a verify read operation to the memory cell CellA3 iscarried out.

First, the bit line BLA3 is precharged with the precharge potential(e.g., about 1.8V). Then, when the level of TGA3 is set at “H” and thetransfer gate TrNA3 is turned on, the bit line BLA3 is electricallyconnected to the data circuit.

When the two select gate lines are applied with Vread, the control gateline (selected word line) CGlU1 of the memory cell CellA3 is appliedwith the read potential Vcgv0 for the verify read operation andunselected word lines are applied with the potential Vread (e.g., about3.5V) with which corresponding memory cells are always turned on, thenthe data of the memory cell CellA3 is transferred to the data circuit2-i by way of the bit line BLA3.

Thereafter, in the data circuit 2-i, an operation for generatingreprogram (Re-write) data and an operation for detecting whether or notprecise data has been completely written into the memory cell CellA3(Program completion detection) are carried out based on the data of thememory cell CellA3 and the program data held by the latch circuitLATCH1.

For example, if “1”-programming is conducted and “0”-programming issufficient, the reprogram (Re-write) data becomes “1” and“0”-programming is not, therefore, conducted to the memory cell CellA3thereafter. Namely, the program operation to the memory cell CellA3 iscompleted.

If “0”-programming is deficient, the reprogram data becomes “0” and“0”-programming to the memory cell CellA3, therefore, continues.

In the verify read operation to the memory cell CellA3, the control gateline CGlU1 is applied with the read potential Vcgv0.

As a result, the memory cells CellA1 and CellA2 having the control gateline CGlU1 common to the memory cells CellA3, CellA1 and CellA2 areturned on, and the program data on the memory cells CellA1 and CellA2held by the bit lines BLA1 and BLA2 are eliminated.

However, since the program data (or reprogram (Re-write) data) on thememory cells CellA1 and CellA2 are held by the bit lines BLB1 and BLB2in the Lower bank, the program data are not completely eliminated.

After the verify read operation, the reprogram (Re-write) data on thememory cell CellA3 is transferred to the bit line BLA3 (actually, sincethe transfer gate TrNA2 is turned on, the reprogram (Re-write) data istransferred to the bit line BLA3 almost simultaneously with the verifyread operation). At this time, the level of TGB3 is “L” and the transfergate TrNB3 is turned off.

Thereafter, when the level of TGB3 is set at “H”, the transfer gateTrNB3 is turned on and the reprogram (Re-write) data on the memory cellCellA3 is also transferred to the bit line BLB3.

If “Step1-12” is completed, the verify read operations to the memorycells CellA1, CellA2 and CellA3 are completed. That is, the reprogram(Re-write) data on the memory cell CellA3 transferred to the bit lineBLA3 in the Upper bank is not eliminated but held by the bit line BLA3.

Thereafter, reprogram operations (the supply of program pulses) to thememory cells CellA1, CellA2 and CellA3 in the Upper bank are conducted.As already described above, the bit line BLA1 in the Upper bank does nothold the program data on the memory cell CellA1 and the bit line BLA2 inthe Upper bank does not hold the program data on the memory cell CellA2.Only the bit line BLA3 in the Upper bank holds the program data on thememory cell CellA3.

Accordingly, before starting the reprogram (Re-write) operations, anoperation for transferring the program data on the memory cell CellA1from the bit line BLB1 in the Lower bank to the bit line BLA1 in theUpper bank (“Step1-13” and “Step1-14”), and an operation fortransferring the program data on the memory cell CellA2 from the bitline BLB2 in the Lower bank to the bit line BLA2 in the Upper bank(“Step1-15” and “Step1-16”) are executed.

(13) Step1-13

In “Step1-13”, the write data on the memory cell CellA1 held by the bitline BLB1 in the Lower bank is transferred to the data circuit 2-i.

First, the level of TGB1 is set at “H” and the transfer gate TrNB1 isturned on. At this time, the write data on the memory cell CellA1 heldby the bit line BLB1 is transferred to the data circuit 2-i. Thisprogram data is latched by the latch circuit LATCH1 in the data circuit2-i (e.g., see FIG. 62).

Thereafter, the level of TGB1 is set at “L” and the transfer gate TrNB1is turned off.

(14) Step1-14

In “Step1-14”, the write data on the memory cell CellA1 held by thelatch circuit LATCH1 in the data circuit 2-i is transferred to the bitline BLA1 in the Upper bank.

First, the level of TGA1 is set at “H” and the transfer gate TrNA1 isturned on. At this time, the bit line BLA1 in the Upper bank iselectrically connected to the data circuit 2-i and the write data on thememory cell CellA1 held by the latch circuit LATCH1 in the data circuit2-i is transferred to the bit line BLA1 in the Upper bank.

Thereafter, the level of TGA1 is set at “L” and the transfer gate TrNA1is turned off.

(15) Step1-15

In “Step1-15”, the write data on the memory cell CellA2 held by the bitline BLB2 in the Lower bank is transferred to the data circuit 2-i.

First, the level of TGB2 is set at “H” and the transfer gate TrNB2 isturned on. At this time, the bit line BLB2 in the Lower bank iselectrically connected to the data circuit 2-i and the write data on thememory cell CellA2 held by the bit line BLB2 is transferred to the datacircuit 2-i. This program data is then latched by the latch circuitLATCH1 in the data circuit 2-i (e.g., see FIG. 62).

Thereafter, the level of TGB2 is set at “L” and the transfer gate TrNB2is turned off.

(16) Step1-16

In “Step1-16”, the write data on the memory cell CellA2 held by thelatch circuit LATCH1 in the data circuit 2-i is transferred to the bitline BLA2 in the Upper bank.

First, the level of TGA2 is set at “H” and the transfer gate TrNA2 isturned on. At this time, the bit line BLA2 in the Upper bank iselectrically connected to the data circuit 2-i, and the write data onthe memory cell CellA2 held by the latch circuit LATCH1 in the datacircuit 2-i is transferred to the bit line BLA2 in the Upper bank.

Thereafter, the level of TGA2 is set at “L” and the transfer gate TrNA2is turned off.

(17) Step1-17

By the time of “Step1-12”, the program data on the memory cell CellA3has been held by the bit line BLA3 in the Upper bank and by theoperations of the “Step1-13”, to “Step1-16”, the program data on thememory cells CellA1 and CellA2 have been transferred to the bit linesBLA1 and BLA2 in the Upper bank.

Thus, each of the bit lines BLA1, BLA2 and BLA3 in the Upper bank turnsinto a state in which the bit line holds reprogram data.

Thereafter, in “Step1-17”, a program pulse is supplied to the selectedcontrol gate line (selected word line) CGlU1 and reprogram (Re-write)operations are executed to the memory cells CellA1, CellA2 and CellA3 inthe Upper bank.

After the supply of program pulses in “Step1-17”, the same operations asthose of “Step1-7” to “Step1-16” are carried out again.

Namely, after the “Step1-17”, the operations of “Step1-7” to “Step1-16”are repeatedly executed until all the selected memory cells have beensufficiently programmed (or the number of program times exceeds apredetermined number of times and a program defect occurs).

As stated so far, according to Concrete Example 2, program operation canbe executed simultaneously to a plurality of memory cells having acommon control gate line in the same bank while using one data circuit.

That is to say, even if the data circuit has only one storage circuitcapable of temporarily holding program/read data on one memory cell, aplurality of memory cells can be programmed using one data circuit byallowing the bit lines to hold the program data on the correspondingmemory cells.

Further, if one data circuit is provided for a plurality of banks and aplurality of memory cells in a certain bank (Upper bank) are programmedusing this data circuit, for example, a plurality of bit lines inanother bank (Lower bank) hold program data.

Accordingly, it is possible to carry out a series of program operations(the supply of a program pulse, the verify read operation, Programcompletion detection and the like) without eliminating the program data.

In this way, according to Concrete Example 2, it is possible to attainhigh-speed programming without increasing the chip area and withoutmaking the size of the data circuit large.

In Concrete Example 2, three memory cells existing in the same bank areprogrammed simultaneously using one data circuit. It is also possible tosimultaneously program four or more memory cells existing in the samebank using one data circuit.

In case of FIG. 78, for example, six bit lines BLA1, BLA2, BLA3, BLC1,BLC2 and BLC3 in the Upper bank and six bit lines BLB1, BLB2, BLB3,BLD1, BLD2 and BLD3 in the Lower bank are connected to one data circuit2-i.

In this case, as in the case of Concrete Example 2, six memory cellsconnected to the six bit lines BLA1, BLA2, BLA3, BLC1, BLC2 and BLC3 inthe Upper bank can be programmed simultaneously. Further, six memorycells connected to the six bit lines BLB1, BLB2, BLB3, BLD1, BLD2 andBLD3 in the Lower bank can be programmed simultaneously.

Further, in case of programming memory cells in the Upper bank, threememory cells connected to the three bit lines BLA1, BLA2 and BLA3 may beprogrammed simultaneously and the bit lines BLB1, BLB2 and BLB3 maystore program data of the bit lines BLA1, BLA2 and BLA3, respectively.

At this time, to prevent capacitive coupling noise between the bitlines, the bit lines BLC1, BLC2 and BLC3 and the bit lines BLD1, BLD2and BLD3 may be used as shield bit lines (which potentials are fixed toVdd or Vss).

Likewise, in case of programming memory cells in the Upper bank, threememory cells connected to the three bit lines BLC1, BLC2 and BLC3 may beprogrammed simultaneously and the bit lines BLD1, BLD2 and BLD3 maystore program data of the bit lines BLC1, BLC2 and BLC3, respectively.At this time, the bit lines BLA1, BLA2 and BLA3 and the bit lines BLB1,BLB2 and BLB3 may be used as shield bit lines.

In case of programming memory cells in the Lower bank, unselected bitlines may be used as shield bit lines, as well.

[Others]

The detailed description of the nonvolatile semiconductor memoryaccording to the present invention is concluded.

In the embodiments, description has been given while taking amulti-level NAND cell type EEPROM as an example. Needless to say, thepresent invention is also applicable to other types of multi-levelmemories. As for a memory cell array, for example, NOR type, AND type(A. Nozoe: ISSCC, Digest of Technical Papers, 1995), DINOR type (S.Kobayashi: ISSCC, Digest of Technical Papers, 1995), Virtual GroundArray type (Lee, et al.: Symposium on VLSI Circuits, Digest of TechnicalPapers, 1994) or the like may be used.

Further, the present invention should not be limited to a flash memoryand is also applicable to a nonvolatile semiconductor memory such as amask ROM and an EPROM.

As described so far, according to the present invention, firstly, atleast one of a plurality of storage circuits used to temporarily storemulti-level data (n-level data) and arranged in a data circuit consistsof a DRAM cell (capacitor). As is well known, the area of the DRAM cellis smaller than that of an SRAM cell. Due to this, if a part of aplurality of storage circuits are constituted by a DRAM cell, the areaof the data circuit can be made smaller than that in the conventionalcase of constituting all storage circuits out of SRAM cells.

Secondly, the word line control circuit consists of a row addressdecoder and a word line driver and the row address decoder is arrangedat one side of the memory cell array. If word line drivers are arrangedat both sides of the memory cell array, respectively, the state of asignal line for connecting the row address decoder at one side of thememory cell array to the word line driver at the other side thereof iscontrolled according to an operation mode. Accordingly, the signal linedoes not influence the operation of memory-cells.

Thirdly, by setting the relationship between, for example, four-leveldata and threshold voltages of memory cells at a predetermined one, evenpage data can be read by conducting two read operations and odd pagedata can be read by conducting one read operation.

Fourthly, the relationship between, for example, four-level data and thethreshold voltages of memory cells at a predetermined one, in, forexample, the program operation to the odd page data conducted after theprogram operation to the even page data, it is possible to shortenprogram time (accelerate program) by completing “00”-programming earlierthan “01”-programming and omitting “00” verify read operation after thecompletion of “00”-programming.

Fifthly, in the program operation, for example, by conducting a refreshoperation to the DRAM cell (capacitor) provided in the data circuitinstead of the latch circuit, the program operation (the supply of aprogram pulse) and the input of program data can be executed inparallel. By doing so, even if the leakage of charges of the capacitorbecomes a problem, precise program operation can be ensured.

Sixthly, by providing a write cache in the data circuit, the programoperation (supply of program pulses) and the input of program data canbe executed in parallel if conducting program operation over a pluralityof pages. This can substantially dispense with data load time after page2, thereby making it possible to accelerate program operation.

Seventhly, if a write cache is provided in the data circuit and thewrite cache consists of a DRAM cell (capacitor), a refresh operation isconducted to the DRAM cell. By doing so, even if the leakage of the DRAMcell causes a problem, it is possible to prevent program data from beingeliminated.

Eighthly, using a data circuit having only one storage circuit capableof storing program/read data on one memory cell, a plurality of memorycells in different banks can be programmed almost simultaneously.Namely, by allowing the bit lines connected to the memory cells to holdthe program data on the memory cells, respectively, a plurality ofmemory cells can be programmed using one data circuit. Further, whileprogramming one memory cell, the other memory cell is subjected to averify read operation. By doing so, program speed can be doubledcompared with the conventional speed without increasing the chip area.

Ninthly, using a data circuit having only one storage circuit capable ofstoring program/read data on one memory cell, a plurality of memorycells arranged in the same bank and having a common control gate linecan be programmed simultaneously. Namely, by allowing bit lines in abank different from the bank in which the bit lines to which the memorycells are connected and the memory cells are arranged, to hold theprogram data on the memory cells, respectively, a plurality of memorycells in the same bank can be programmed simultaneously using one datacircuit. This can accelerate program speed compared with theconventional speed without increasing the chip area.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A nonvolatile semiconductor memory comprising: a first string lineincluding a first memory cell and a first select transistor connected inseries; a second string line including a second memory cell and a secondselect transistor connected in series; a first bit line connected tosaid first string line; a second bit line connected to said secondstring line, being extended to a direction different from a direction inwhich the first bit line is extended; a common node connected to oneends of said first and second bit lines; and a common latch circuitconnected to said common node, wherein first program data of said firstmemory cell is latched in said common latch circuit and second programdata of said second memory cell is held by said second bit line, duringa verify read of said first memory cell is executed.
 2. The nonvolatilesemiconductor memory according to claim 1, wherein said first memorycell and said second memory cell are connected to different word lines.3. The nonvolatile semiconductor memory according to claim 1, wherein apotential of a bit line adjacent to one of said first bit line and saidsecond bit line is set at a fixed potential.
 4. The nonvolatilesemiconductor memory according to claim 3, wherein said fixed potentialis one of a ground potential and a power supply potential.
 5. Thenonvolatile semiconductor memory according to claim 1, wherein each ofsaid first and second string lines comprises a NAND cell unit.
 6. Anonvolatile semiconductor memory comprising: a first string lineincluding a first memory cell and a first select transistor connected inseries; a first bit line connected to said first string line; a secondbit line, being extended to a direction different from a direction inwhich the first bit line is extended; a common node connected to oneends of said first and second bit lines; and a common latch circuitconnected to said common node, wherein first program data of said firstmemory cell is latched in said common latch circuit and second programdata of said second memory cell is held by said second bit line, duringa verify read of said first memory cell is executed.
 7. The nonvolatilesemiconductor memory according to claim 6, wherein said first memorycell and said second memory cell are connected to different word lines.8. The nonvolatile semiconductor memory according to claim 6, wherein apotential of a bit line adjacent to one of said first bit line and saidsecond bit line is set at a fixed potential.
 9. The nonvolatilesemiconductor memory according to claim 8, wherein said fixed potentialis one of a ground potential and a power supply potential.
 10. Thenonvolatile semiconductor memory according to claim 6, wherein saidfirst string line comprises a NAND cell unit.
 11. A nonvolatilesemiconductor memory comprising: a first string line including a firstmemory cell and a first select transistor connected in series; a secondstring line including a second memory cell and a second selecttransistor connected in series; a first bit line connected to said firststring line; a second bit line connected to said second string line,being extended to a direction different from a direction which the firstbit line is extended; a common node connected to one ends of said firstand second bit lines; and a common latch circuit connected to saidcommon node, wherein program data of said first memory cell is latchedin said common latch circuit and program/read data of said second memorycell is held by said second bit line, during a programming of said firstmemory cell is executed.
 12. The nonvolatile semiconductor memoryaccording to claim 11, wherein said first memory cell and said secondmemory cell are connected to different word lines.
 13. The nonvolatilesemiconductor memory according to claim 11, wherein a potential of a bitline adjacent to one of said first bit line and said second bit line isset at a fixed potential.
 14. The nonvolatile semiconductor memoryaccording to claim 13, wherein said fixed potential is one of a groundpotential and a power supply potential.
 15. The nonvolatilesemiconductor memory according to claim 11, wherein each of said firstand second string lines comprises a NAND cell unit.
 16. A nonvolatilesemiconductor memory comprising: a first string line including a firstmemory cell and a first select transistor connected in series; a firstbit line connected to said first string line; a second bit line, beingextended to a direction different from a direction in which the firstbit line is extended; a common node connected to one ends of said firstand second bit lines; and a common latch circuit connected to saidcommon node, wherein program data of said first memory cell is latchedin said common latch circuit and program/read data of said second memorycell is held by said second bit line, during a programming of said firstmemory cell is executed.
 17. The nonvolatile semiconductor memoryaccording to claim 16, wherein said first memory cell and said secondmemory cell are connected to different word lines.
 18. The nonvolatilesemiconductor memory according to claim 16, wherein a potential of a bitline adjacent to one of said first bit line and said second bit line isset at a fixed potential.
 19. The nonvolatile semiconductor memoryaccording to claim 18, wherein said fixed potential is one of a groundpotential and a power supply potential.
 20. The nonvolatilesemiconductor memory according to claim 16, wherein said first stringline comprises a NAND cell unit.
 21. The nonvolatile semiconductormemory according to claim 1, wherein the first bit line is provided in afirst bank, and the second bit line is provided in a second bankdifferent from the first bank.
 22. The nonvolatile semiconductor memoryaccording to claim 6, wherein the first bit line is provided in a firstbank, and the second bit line is provided in a second bank differentfrom the first bank.
 23. The nonvolatile semiconductor memory accordingto claim 11, wherein the first bit line is provided in a first bank, andthe second bit line is provided in a second bank different from thefirst bank.
 24. The nonvolatile semiconductor memory according to claim16, wherein the first bit line is provided in a first bank, and thesecond bit line is provided in a second bank different from the firstbank.